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Title: Middle American Frogs of the Hyla microcephala Group
Author: Duellman, William E., 1930-, Fouquette, M. J.
Language: English
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University of Kansas Publications

Museum of Natural History

Volume 17, No. 12, pp. 517-557, pls. 13-16, 9 figs.
March 20, 1968

Middle American Frogs
of the Hyla microcephala Group

BY

WILLIAM E. DUELLMAN AND M. J. FOUQUETTE, JR.

University of Kansas
Lawrence
1968



University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Frank B. Cross

Volume 17, No. 12, pp. 517-557, 4 pls. 9 figs.
Published March 20, 1968

University of Kansas
Lawrence, Kansas

PRINTED BY
ROBERT R. (BOB) SANDERS, STATE PRINTER
TOPEKA, KANSAS
1968

31-9419



Middle American Frogs
of the Hyla microcephala Group

BY
WILLIAM E. DUELLMAN AND M. J. FOUQUETTE, JR.


CONTENTS


                                                                 PAGE

Introduction                                                      519
  Acknowledgments                                                 520
  Materials and Methods                                           520

Hyla microcephala Group                                           521
  Key to Species and Subspecies                                   522

Accounts of Species and Subspecies                                523

Cranial Osteology                                                 540

Analysis of Mating Calls                                          544

Life History                                                      550

Phylogenetic Relationships                                        552

Literature Cited                                                  556



INTRODUCTION


The small yellow tree frogs, _Hyla microcephala_ and its relatives,
are among the most frequently heard and commonly collected frogs in
the lowlands of southern México and Central America. The similarities
in size, proportions, and coloration of the different species have
resulted not so much in a multiplicity of specific names, but in
differences of opinion on the application of existing names to the
various taxa. For example, the populations on the Atlantic lowlands
have been known by three names, two of which have been applied to
other taxa. Much of the confusion has been the result of previous
workers' unfamiliarity with the animals in life and unawareness of the
intraspecific geographic variation in the most widespread species.

Independently we undertook studies of these frogs in the field. The
second author worked on the interspecific relationships and isolating
mechanisms in Panamá (Fouquette, 1960b) and later studied the species
in southern México. As part of his survey of the hylids of Middle
America, the first author accumulated field and laboratory data on the
frogs throughout their ranges in México and Central America. The
purpose of this report is to present our findings on the four species
of Middle American frogs that we place in the _Hyla microcephala_
group. In addition to conventional taxonomic characters, we have
utilized the features of the cranial osteology and have relied heavily
on the data obtained from an analysis of the mating calls.
Furthermore, we have included ecological and distributional data in
our synthesis of interspecific relationships.


ACKNOWLEDGMENTS

Examination of specimens was made possible by the provision of working
space at various institutions or through the loan of specimens. For
their generosity in this manner we are grateful to Richard J. Baldauf,
Charles M. Bogert, James E. Böhlke, Doris M. Cochran, Robert F. Inger,
John M. Legler, Alan E. Leviton, Gerald Raun, Jay M. Savage, Hobart M.
Smith, Robert C. Stebbins, Wilmer W. Tanner, Charles F. Walker, Ernest
E. Williams, and Richard G. Zweifel.

Duellman is especially grateful to Charles W. Myers, Linda Trueb,
Jerome B. Tulecke, and John Wellman for their assistance in the field
and to Linda Trueb for her work on the cranial osteology that is
incorporated in this report. Fouquette is indebted to H. Morgan Smith
and A. C. Collins for assistance in the field, to A. J. Delahoussaye
for assistance in the laboratory, and to W. Frank Blair for use of the
facilities of the sound laboratory at the University of Texas and for
much help in the early stages of this study.

The research reported herein was accomplished mainly through support
by the National Science Foundation (grants NSF G-9827 and GB-1441 to
Duellman and GB-599 to Fouquette). The latter's field work in México
was assisted in part by NSF Grant G-4956 to W. Frank Blair. Some of
the field studies carried out in Panamá by Duellman were supported by
a grant from the National Institutes of Health (NIH GM-12020).

We are grateful to many persons, too numerous to mention, who in
various ways aided our field work in Middle America. We are especially
indebted to Dr. Rodolfo Hernandez Corzo and the late Ing. Luis Macías
Arellano of the Dirección General de la Fauna Silvestre of the Mexican
government for providing permits to collect in México.


Materials and Methods

For this report, data has been obtained from 2829 preserved frogs, 42
skeletal preparations, 8 lots of tadpoles and young, and 4 lots of
eggs. Much of the material was collected in our independent field
work, which has extended over a period of 11 years.

Measurements were taken in the manner described by Duellman (1956).
Osteological data were obtained from specimens that were cleared in
potassium hydroxide, stained with alizarin red, and stored in
glycerine. Recordings were made by means of Magnemite portable tape
recorders (Amplifier Corp. America). The calls recorded by Fouquette
were analyzed on a Sonagraph (Kay Electric Co.) at the University of
Texas; those recorded by Duellman were analyzed mainly on a Vibralyzer
(Kay Electric Co.) at the University of Kansas and in part on a
Sonagraph at the University of Southwestern Louisiana. Sample calls
were analyzed on all three instruments; the slight differences in
results were found to be less than the error in measurement, so the
data from all sources were combined without correction. The techniques
and terminology of the calls are those defined by Fouquette (1960a,
1960b).

In the accounts of the species we have attempted to give a complete
synonymy. At the end of each species account the localities from which
specimens were examined are listed alphabetically within each state,
province, or department, which in turn are listed alphabetically
within each country. The countries are arranged from north to south.
Localities preceded by an asterisk (*) are not plotted on the
accompanying maps due to the crowding of symbols that would have
resulted. Abbreviations for museum specimens are listed below:

  AMNH --American Museum of Natural History
  ANSP --Academy of Natural Sciences of Philadelphia
  BMNH --British Museum (Natural History)
  BYU  --Brigham Young University
  CAS  --California Academy of Sciences
  FMNH --Field Museum of Natural History
  KU   --University of Kansas Museum of Natural History
  MCZ  --Museum of Comparative Zoology
  MVZ  --Museum of Vertebrate Zoology
  SU   --Stanford University
  UIMNH--University of Illinois Museum of Natural History
  UMMZ --University of Michigan Museum of Zoology
  USC  --University of Southern California
  USNM --United States National Museum
  UU   --University of Utah
  TCWC --Texas Cooperative Wildlife Collection
  TNHM --Texas Natural History Museum



HYLA MICROCEPHALA GROUP


_Definition._--Small hylids attaining a maximum snout-vent length of
27 mm. in males and 32 mm. in females; dorsum yellowish tan with brown
markings; thighs uniformly yellow, vocal sac in breeding males yellow;
snout truncate in lateral profile; tympanum distinct, usually slightly
smaller than one-half diameter of eye; vocal sac single, median,
subgular; fingers about one-third webbed; toes webbed nearly to bases
of discs, except only to middle of antepenultimate or base of
penultimate phalanx of fourth toe; tarsal fold weak; inner metatarsal
tubercle low, flat, elliptical; axillary membrane present; pupil
horizontally elliptical; palpebral membrane unmarked; cranial elements
reduced in ossification; sphenethmoid small, short; frontoparietal
fontanelle large; tegmen tympani not extensive; quadratojugal greatly
reduced; anterior arm of squamosal extending only about one-fourth
distance to maxillary; posterior arm of squamosal not having bony
connection with proötic; nasals lacking maxillary processes; medial
ramus of pterygoid not having bony attachment to proötic; maxillary,
premaxilary, and prevomerine teeth present; palatine and parasphenoid
teeth absent; Mentomeckelians ossified; tadpoles having xiphicercal
tails with deep caudal fins and terminal mouth lacking teeth; mating
call consisting of one primary note followed by a series of shorter
secondary notes; haploid number of chromosomes, 15 (known only in _H.
microcephala_ and _H. phlebodes_.)

_Content._--As recognized here the _Hyla microcephala_ group contains
four species, one having two subspecies. An alphabetical list of the
specific and subspecific names that we consider to be applicable to
the _Hyla microcephala_ group are listed below.


           Names Proposed                        Valid Names

_Hyla cherrei_ Cope, 1894             ? = _H. m. microcephala_
_Hyla microcephala_ Cope, 1886          = _H. m. microcephala_
_Hyla microcephala_ Boulenger,
  1898 (_nec_ Cope, 1886)               = _H. microcephala underwoodi_
_Hyla microcephala martini_ Smith, 1951 = _H. microcephala underwoodi_
_Hyla microcephala sartori_ Smith, 1951 = _H. sartori_
_Hyla phlebodes_ Stejneger, 1906        = _H. phlebodes_
_Hyla robertmertensi_ Taylor, 1937      = _H. robertmertensi_
_Hyla underwoodi_ Boulenger, 1899       = _H. microcephala underwoodi_


_Discussion._--The color pattern is the most useful character in
distinguishing the species of the _Hyla microcephala_ group from one
another. Except in _Hyla microcephala_, little geographic variation in
color pattern is noticeable. The features of color pattern that are
helpful in identifying the species are: 1) presence or absence of
lateral dark brown stripe; 2) longitudinal extent and width of lateral
stripe, if present; 3) presence or absence of a narrow white line just
dorsal to the lateral dark stripe; 4) presence or absence of an
interorbital dark mark; 5) the arrangement of dark markings on the
back, either as longitudinal lines or series of dashes, or in the form
of various kinds of transverse markings; 6) presence of dark flecks,
longitudinal line, or transverse marks on shanks.

Few consistent differences in measurements and proportions exist among
the species (Table 1). The most obvious morphological difference is
that the head is noticeably narrower in _H. robertmertensi_ than in
the other species. _Hyla phlebodes_ is the smallest species; adult
males attain snout-vent lengths of only 23.6 mm. The body is slender
in _H. microcephala_ and _robertmertensi_, slightly wider in
_phlebodes_, and noticeably broader in _sartori_.

_Distribution._--The composite range of the Middle American frogs of
the _Hyla microcephala_ group includes the lowlands of southern México
and Central America, in some places to elevations of 1200 meters,
southeastward from southern Jalisco and southern Veracruz, excluding
arid regions (northern Yucatán Peninsula, Balsas-Tepalcatepec Basin,
Plains of Tehuantepec, Grijalva Valley, Salamá Basin, and upper
Motagua Valley) to the Pacific lowlands and the Cauca and Magdalena
valleys in Colombia.


Key to Species and Subspecies


1. Lateral dark stripe, bordered above by narrow white line,
     extending from snout at least to sacral region                  2

   Lateral dark stripe, if present, not extending posteriorly to
     sacral region and not bordered above by narrow white line       4

2. Lateral dark stripe continuous to groin; dark flecks or
     longitudinal line on shanks; interorbital dark bar absent;
     dorsal pattern usually consisting of pair of longitudinal dark
     lines or series of dashes                                       3

   Lateral dark stripe usually extending only to sacral region;
     dark transverse bars on shanks; interorbital bar usually
     present; dorsal pattern usually consisting of interconnecting
     dark lines, sometimes forming transverse marks
                                       _H. microcephala underwoodi_

3. Lateral dark stripe narrow, covering only upper edge of
     tympanum; dorsal longitudinal stripes continuous, extending to
     vent                              _H. microcephala microcephala_

   Lateral dark stripe wide, encompassing entire tympanum; dorsal
     markings consisting of longitudinal series of flecks or dashes,
     or of two lines, usually not extending to vent _H. robertmertensi_

4. Lateral dark stripe indistinct, present only above tympanum and
     insertion of arm; dorsal markings consisting of narrow lines
     and dashes, sometimes interconnected; transverse bars on shanks
     narrow relative to interspaces                     _H. phlebodes_

   Lateral dark stripe absent; dorsal markings consisting of two broad
     chevron-shaped marks; transverse bars on shanks wide relative to
     interspaces                                          _H. sartori_



ACCOUNTS OF SPECIES AND SUBSPECIES


_Hyla microcephala_ Cope


_Diagnosis._--Lateral dark stripe narrow, covering only upper edge of
tympanum, bordered above by narrow white stripe; dorsal pattern
consisting of pair of longitudinal brown lines and no interorbital bar
(eastern populations), or of irregular dark markings forming an X- or
)(-shaped mark in scapular region and an interorbital bar (western
populations).

_Content._--The populations inhabiting the Pacific lowlands of
southeastern Costa Rica eastward to Colombia are recognized herein as
_Hyla microcephala microcephala_ Cope; the populations in western
Costa Rica northward to México are assigned to _Hyla microcephala
underwoodi_ Boulenger.

_Distribution._--Southern Veracruz and northern Oaxaca southeastward
through the Atlantic lowlands of Central America to north-central
Nicaragua, thence southeastward on the Pacific lowlands to eastern
Panamá, and thence into the Cauca and Magdalena valleys (Caribbean
drainage) of Colombia (Fig. 1).


  [Illustration: Fig. 1. Map showing locality records for _Hyla
        microcephala_.]


Table 1.--Variation in Certain Measurements and Properties in the
  Hyla microcephala Group. (All Data Based on Adult Males;
  Mean and Standard Error of Mean Below Observed Range.)

========================================================================
  Locality               | N  |  Snout-vent | Tibia length |Foot length|
                         |    |   length    | ------------ | --------- |
                         |    |   (S-V L)   |    S-V L     |   S-V L   |
------------------------------------------------------------------------
                         |       _H. m. microcephala_
                         |
Panamá: Canal Zone       | 25 | 21.5-24.1   | 50.2-56.0    | 40.9-46.6 |
                         |    | 22.8±0.20   | 52.9±0.37    | 43.5±0.28 |
                         |    |             |              |           |
Costa Rica: Golfito      | 25 | 18.5-24.5   | 49.1-54.4    | 41.8-48.0 |
                         |    | 22.4±0.27   | 51.6±0.26    | 45.1±0.32 |
                         |
                         |       _H. m. underwoodi_
                         |    |
Nicaragua: La Cumplida   | 25 | 23.0-25.6   | 51.0-55.7    | 41.3-46.5 |
                         |    | 24.1±0.19   | 52.9±0.25    | 43.7±0.25 |
                         |    |             |              |           |
Guatemala: Finca Chamá   | 25 | 21.8-25.0   | 51.0-57.2    | 41.2-47.8 |
                         |    | 23.5±0.16   | 54.3±0.39    | 44.4±0.30 |
                         |    |             |              |           |
Tabasco: Teapa           | 25 | 22.7-25.8   | 48.0-54.5    | 40.7-46.8 |
                         |    | 24.3±0.14   | 51.5±0.29    | 43.3±0.25 |
                         |    |             |              |           |
Oaxaca: Donají-Sarabia   | 25 | 22.1-25.9   | 49.8-55.6    | 40.5-46.6 |
                         |    | 23.8±0.19   | 52.8±0.33    | 43.4±0.27 |
                         |    |             |              |           |
Veracruz: Alvarado       | 25 | 21.9-25.4   | 49.6-54.4    | 40.7-47.5 |
                         |    | 24.1±0.17   | 51.1±0.28    | 42.6±0.34 |
                         |
                         |       _H. robertmertensi_
                         |
Guatemala: La Trinidad   | 21 | 21.8-24.6   | 47.1-52.8    | 40.9-51.3 |
                         |    | 23.4±0.15   | 49.9±0.34    | 43.5±0.17 |
                         |    |             |              |           |
Chiapas: Acacoyagua      | 25 | 21.4-25.7   | 47.8-52.4    | 41.7-46.3 |
                         |    | 24.1±0.20   | 50.4±0.45    | 43.9±0.23 |
                         |    |             |              |           |
Oaxaca: Tapanatepec      | 25 | 22.4-26.4   | 44.1-48.3    | 39.1-44.5 |
                         |    | 24.7±0.18   | 46.4±0.23    | 41.7±0.23 |
                         |
                         |       _H. phlebodes_
                         |
Panamá: Canal Zone       | 25 | 19.6-23.2   | 49.1-56.9    | 41.9-47.1 |
                         |    | 22.2±0.16   | 52.8±0.35    | 45.4±0.26 |
                         |    |             |              |           |
Costa Rica: Turrialba    | 25 | 19.7-23.6   | 47.4-55.7    | 38.1-46.4 |
                         |    | 22.0±0.18   | 51.1±0.35    | 42.8±0.38 |
                         |
                         |       _H. sartori_
                         |
Guerrero: Tierra Colorada| 25 | 23.7-26.0   | 47.2-51.4    | 42.4-47.8 |
                         |    | 24.8±0.13   | 49.6±0.23    | 45.2±0.27 |
------------------------------------------------------------------------
Table 1. (continued)
===============================================================
  Locality               | Head length | Head width | Tympanum
                         | ----------- | ---------- | --------
                         |  S-V L      |   S-V L    |   Eye
---------------------------------------------------------------
                         |       _H. m. microcephala_
                         |
Panamá: Canal Zone       | 28.5-32.8   | 28.1-30.9  | 44.0-54.1
                         | 31.0±0.22   | 29.4±0.11  | 49.0±0.55
                         |
Costa Rica: Golfito      | 30.2-35.5   | 29.0-32.7  | 40.0-57.8
                         | 33.1±0.25   | 30.8±0.16  | 48.4±1.10
                         |
                         |       _H. m. underwoodi_
                         |
Nicaragua: La Cumplida   | 29.7-33.5   | 28.9-31.8  | 42.3-60.0
                         | 31.6±0.19   | 30.4±0.17  | 49.3±0.97
                         |
Guatemala: Finca Chamá   | 30.8-35.3   | 29.6-33.6  | 37.5-56.4
                         | 33.0±0.16   | 31.3±0.36  | 45.2±0.89
                         |
Tabasco: Teapa           | 29.5-33.0   | 28.7-31.8  | 40.7-53.8
                         | 31.7±0.17   | 30.3±0.16  | 45.5±0.38
                         |
Oaxaca: Donají-Sarabia   | 30.4-34.8   | 28.9-32.6  | 37.0-54.1
                         | 32.8±0.19   | 30.8±0.17  | 45.1±0.76
                         |
Veracruz: Alvarado       | 29.9-33.8   | 29.1-32.9  | 40.7-53.8
                         | 31.4±0.18   | 30.5±0.17  | 46.6±0.65
                         |
                         |       _H. robertmertensi_
                         |
Guatemala: La Trinidad   | 30.0-33.3   | 27.3-29.8  | 44.4-50.0
                         | 31.3±0.20   | 28.5±0.23  | 47.4±0.46
                         |             |            |
Chiapas: Acacoyagua      | 29.1-32.7   | 26.0-30.3  | 42.8-53.8
                         | 31.2±0.29   | 28.1±0.20  | 46.5±0.50
                         |             |            |
Oaxaca: Tapanatepec      | 26.1-30.4   | 25.4-28.1  | 45.8-58.3
                         | 28.4±0.16   | 26.8±0.14  | 52.9±0.77
                         |
                         |       _H. phlebodes_
                         |
Panamá: Canal Zone       | 33.6-37.4   | 32.3-36.0  | 37.9-46.4
                         | 34.8±0.18   | 33.8±0.18  | 41.6±0.49
                         |             |            |
Costa Rica: Turrialba    | 32.6-35.9   | 30.5-35.0  | 35.7-48.2
                         | 34.1±0.16   | 32.9±0.17  | 40.1±0.53
                         |
                         |       _H. sartori_
                         |
Guerrero: Tierra Colorada| 29.4-31.8   | 28.9-31.0  | 42.3-52.0
                         | 30.6±0.13   | 30.0±0.12  | 47.4±0.59
---------------------------------------------------------------



_Hyla microcephala microcephala_ Cope


  _Hyla microcephala_ Cope, Proc. Amer. Philos. Soc., 23:281, February
      11, 1886 [Syntypes.--USNM 13473 (2 specimens, now lost) from
      Chiriquí, Panamá; Mr. MacNeil collector]; Bull. U.S. Natl. Mus.,
      32:14, 1887. Günther, Biologia-Centrali Americana, Reptilia and
      Batrachia, p. 265, June, 1901. Dunn, Occas. Papers Boston Soc.
      Nat. Hist., 5:413, October 10, 1931; Occas. Papers Boston Soc.
      Nat. Hist., 8:72, June 7, 1933. Stebbins and Hendrickson, Univ.
      California Publ. Zool., 56:524, February 17, 1959. Fouquette,
      Evolution, 14:484, December 16, 1960. Busack, Copeia, 2:371,
      June 21, 1966.

  ? _Hyla cherrei_ Cope, Proc. Acad. Nat. Sci. Philadelphia, 1894,
      p. 195, 1894 [Holotype.--location unknown, apparently lost;
      type-locality: "Alajuela, Costa Rica;" R. Alfaro collector].
      Günther, Biologia Centrali-Americana: Reptilia and Batrachia,
      p. 264, June, 1901. Taylor, Univ. Kansas Sci. Bull., 35:846,
      July 1, 1952.

  _Hyla underwoodi_, Ruthven, Misc. Publ. Mus. Zool., Univ. Michigan,
      8:55, September 15, 1922. Barbour, Proc. New England Zool. Club,
      10:31, March 2, 1928.

  _Hyla microcephala microcephala_, Smith, Herpetologica, 7:185,
      December 31, 1951. Taylor, Univ. Kansas Sci. Bull., 39:23,
      November 18, 1958.


_Diagnosis._--Brown lateral stripe narrow, extending from nostril
along canthus, along upper edge of tympanum to groin, bordered above
by narrow white line; pair of dark brown longitudinal lines on dorsum
extending to vent; shanks having dark longitudinal line or flecks, no
transverse bars; interorbital dark mark lacking.

_Description and Variation._--The color pattern is nearly constant. Of
103 males from the Canal Zone, all lack an interorbital dark bar, and
all have a dark longitudinal line on the dorsal surface of the shank
and a narrow lateral dark stripe, bordered above by a narrow white
line, extending to the groin. The longitudinal dark lines on the
dorsum are continuous to the groin in 95 specimens and fragmented in
two specimens. In two others the lines converge and fuse in the
scapular region, and in four specimens auxiliary, fragmented lines are
present dorsolaterally.

In all specimens from southeastern Costa Rica (Golfito, Palmar Sur,
and Villa Neilly) the pattern is constant, except that in about 10 per
cent of the specimens the longitudinal line on the dorsal surface of
the shank is replaced by a row of brown flecks.

Of the limited number of Colombian specimens examined, all are
patterned normally, except three from Sautata, Chocó, three from
Curumani, and three from Arcataca, Magdalena, which have flecks on the
dorsal surfaces of the shanks, and one from Espinal, Tolima, which has
no markings on the shanks.

When active at night most individuals are pale yellowish tan dorsally;
the white dorsolateral line is noticeable, but the brown lateral
stripe, dorsal brown lines, and lines on shanks are so pale that often
they are barely discernible. By day the dorsum changes to tan or pale
reddish brown; the stripes are dark brown, and the dorsolateral stripe
that is white at night becomes creamy yellow (Pl. 13). Small brown
flecks are present on the dorsum of most individuals. The venter
always is white, and the iris is pale bronze with a brown tint
immediately anterior and posterior to the pupil. In breeding males the
vocal sac is pale yellow.

_Tadpoles._--Tadpoles of this species have been found in weed-choked
ponds in eastern Panamá Province. The following description is based
on KU 104097, a specimen in developmental stage 34 (Gosner, 1960).

Total length, 20.5 mm.; body length, 8.2 mm.; body slightly wider
than deep; snout pointed; nostrils large, situated dorsally, much
closer to snout than eyes, directed anteriorly; eyes moderately
small, situated dorsolaterally and directed laterally; spiracle
sinistral, located just posteroventral to eye; anal tube dextral.
Tail xiphicercal; caudal musculature moderately deep, becoming
slender posteriorly, extending beyond caudal fin; fins deepest at
about one-third distance from body to tip of tail; dorsal fin
extending onto body, deeper than deepest part of caudal
musculature; ventral fin slightly shallower than musculature.
Mouth small, terminal, lacking teeth and fringing papillae, but
having finely serrate beaks. In preservative, top of head pale
brown; dark stripe from tip of snout through eye to posterior edge
of body, narrowing to thin line on proximal one-fourth of tail;
venter white; tail creamy tan with fine black flecks most numerous
posteriorly; posterior two-thirds of fins edged with black. In
life, top of head yellowish tan; lateral stripe brown; belly
white; anterior half of tail lacking pigment; posterior half deep
orange; iris pale bronze (Pl. 15).

_Remarks._--Evidence for intergradation of _Hyla microcephala_ with
_H. underwoodi_ is provided by four specimens [USC 818 (2), 6081-2]
from 6.1 kilometers northeast of the mouth of the Río Tarcoles, and
nine specimens [USC 8254 (2), 8255, 8256 (4), 8258 (2)] from Parrita,
both in Puntarenas Province, Costa Rica. These localities lie about
two-thirds the distance from the northwesternmost locality for _H.
m. microcephala_ (Palmar Sur) to the southeasternmost locality for
_H. m. underwoodi_ (Barranca). Although in most aspects of coloration
the frogs are more nearly like _H. m. underwoodi_ than _H. m.
microcephala_, some specimens have longitudinal lines on their shanks,
such as are characteristic of _H. m. microcephala_. The dorsal pattern
varies from nearly complete longitudinal lines to broken lines, fused
into an X-shaped scapular mark or not.

As noted by Rivero (1961:135), _Hyla microcephala_ seems to be closely
related to _Hyla misera_ Werner, a species having a wide distribution
east of the Andes in South America. Despite the similarity in color
pattern, size, and structure, we are reluctant to place the two taxa
in the same species until data on coloration in life, mating calls,
and life history are available for _Hyla misera_ and compared with
those of _Hyla microcephala_.

The status of Cope's _Hyla cherrei_ is questionable. Since the type,
the only specimen ever referred to the species, apparently is lost,
the only extant information regarding the taxon is contained in the
original description (Cope, 1894). There the species was characterized
as having a narrow dorsolateral white stripe and lacking pigment on
the upper arms and thighs. These characteristics of the color pattern
combined with the statements "vomerine teeth few, opposite the middle
of the very large choanae" and "tympanic drum distinct, one half the
area of eye" serve to distinguish _H. cherrei_ from all other Costa
Rican hylids, except _H. m. microcephala_ and _H. m. underwoodi_. No
statements in the type description will definitely associate _cherrei_
with one or the other of these subspecies. Since it seems obvious that
_H. cherrei_ can be associated with _H. microcephala_, we prefer to
place the name in the synonymy of the nominate subspecies, thereby
preserving the commonly used name _H. underwoodi_ (Boulenger, 1899) as
a subspecies of _H. microcephala_.

_Distribution._--_Hyla microcephala microcephala_ inhabits coastal
lowlands from the area of Golfo Dulce (apparently absent from the
Osa Peninsula) in southeastern Costa Rica eastward in Panamá,
including the Azuero Peninsula to northern Colombia and thence
southward in the valleys of the Río Cauca and Río Magdalena in
Colombia (Fig. 1). Except for the central area of the Canal Zone
the subspecies is unknown from the Caribbean drainage in Central
America, but in Colombia the subspecies occurs only in the
Caribbean drainage. In Central America this frog occurs mostly on
the coastal lowlands; the highest recorded elevation is 560 meters
at El Valle, Coclé, Panamá. Throughout most of its range _Hyla
microcephala microcephala_ occurs in disturbed habitats--cut-over
forests, secondary growth, and pastureland. It does not seem to be
an inhabitant of either primary forest or of _Curatella_-savanna.

_Specimens examined._--522, as follows: +Costa Rica+: Puntarenas:
Golfito, KU 32172-207; 3 km. E Golfito, KU 86399, USC 2757-8;
Palmar Sur, KU 64591-608, USC 2650 (14), UU 3907-32; *1.5-2.5 km.
ESE Palmar Sur, KU 68293-7 (skeletons), 93957-62; Parrita, USC
8254 (2), 8255, 8256 (4), 8258 (2) [intergrades with _H. m.
underwoodi_]; 3 km. NW Piedras Blancas, KU 103689; 6.1 km. NE
mouth of Río Tárcoles, USC 818 (2), 6081-2 [intergrades with _H.
m. underwoodi_]; Villa Neilly, USC 2651; *1-5 km. WNW Villa
Neilly, USC 6182-4, 8003 (4), 8031 (3), 8032; *10.5 km. WNW Villa
Neilly, KU 64609-27, 68398 (eggs).

+Panama+: Canal Zone: Albrook Air Base, TNHC 23389, 23497; Balboa,
ANSP 19555-6; *Fort Clayton, UIMNH 42008-12; *2.8 km. SW Fort
Kobbe, KU 96015-25; *Frijoles, MCZ 19208; *Bamboa, MCZ 21507; *8.3
km. N Gatún Locks, TNHC 23441; *Juan Diaz, MCZ 13747; *Juan Mina,
AMNH 55436-7, ANSP 21811-2, UMMZ 126734, 126735 (6), UU 3900-6;
*8-14 km. N Miraflores Locks, TNHC 23374-88, 23390-409, 23411-38,
23440, 23442-60, 23462-76; 23478-83, 23492, 23555-60, 23562-76;
*Río Chagres, AMNH 55430, 55439; *Río Cocolí, 3.5 km. N Miraflores
Locks, TNHC 23410; *Summit, ANSP 23365-71, FMNH 22966-9, KU
97783-87. Chiriqui: 5.5 km. E Concepción, AMNH 69772; *14.4 km. E
Concepción, AMNH 69773-8; 2 km. S David, AMNH 69779; *Progreso,
UMMZ 58252, 58253 (2), 58254, 58436; Río Gariché, 8.3 km. ESE Paso
Canoas, KU 103065-8. Coclé: 1 km. SE El Caño, KU 103042-51; El
Valle de Antón, AMNH 59614-18 (10), 69785, ANSP 23502-5, KU
77201-14, MVZ 66578-83, UIMNH 46532. Colón: Cement Plant,
Transisthmian Highway, FMNH 60394-5. Darién: El Real, KU 80454-5,
103052-64, UMMZ 125036 (10), USNM 140567-8; Río Canclon at Río
Chucunaque, UMMZ 125035; *Río Chucunaque, near Yavisa, AMNH 59523.
Los Santos: Tonosí, KU 101606-9. Panamá: 5 km. S Bejuco, AMNH
69782; 3 km. W Chepo, KU 77172-4, 104097-8 (tadpoles); *6 km. WSW
Chepo, KU 77175; *Chico, Río La Jagua, USNM 129070; *La Joya,
Cacora, ANSP 25129-33; Madden Dam, FMNH 67819; Nueva Gorgona, AMNH
69780-1; *1.6 km. W Nueva Gorgona, AMNH 69783-4; 1.5 km. W Pacora,
77176-200; *Río La Laja, near Chamé, ANSP 21845; *Río Tapia, MCZ
10048; *Tapia, AMNH 18930, 18950, 18952-3; *18 km. E Tocumen, MVZ
78662.

+Colombia+: Chocó: Sautatá, Atrato, FMNH 74918 (2), 74919.
Magdalena: Aracataca, ANSP 19755-7; Curumani, MCZ 21465-74, UIMNH
28855; UMMZ 90168, USNM 118247; El Banco, Río Magdalena, ANSP
25061; Fundación, UMMZ 48281-2. Tolima: Espinal, MCZ 15068;
Mariquita, FMNH 81822-3. Valle: Sevilla, MCZ 13751-3.



_Hyla microcephala underwoodi_ Boulenger


  _Hyla microcephala_ Boulenger, Proc. Zool. Soc. London, p. 481,
      October 1, 1898 [Syntypes.--BMNH 94. 11. 1532-33 from Bebedero,
      Guanacaste Province, Costa Rica; C. F. Underwood collector] (not
      _Hyla microcephala_ Cope, Proc. Amer. Philos. Soc., 23:281,
      February 11, 1886, from Chiriquí, Panamá).

  _Hyla underwoodi_ Boulenger, Ann. Mag. Nat. Hist., ser. 7, 3:277,
      April, 1899 (substitute name for _Hyla microcephala_ Boulenger,
      preoccupied). Günther, Biologia-Centrali Americana, Reptilia and
      Batrachia, p. 278, September, 1901. Dunn and Emlen, Proc. Acad.
      Nat. Sci. Philadelphia, 84:25, March 22, 1932. Stuart, Misc. Publ.
      Mus. Zool., Univ. Michigan, 29:39, October 1, 1935. Taylor, Proc.
      Biol. Soc. Washington, 50:44, April 21, 1937. Stuart, Occas.
      Papers Mus. Zool., Univ. Michigan, 471:15, May 17, 1943. Taylor
      and Smith, Proc. U. S. Natl. Mus., 95:586, June 30, 1945. Stuart,
      Misc. Publ. Mus. Zool., Univ. Michigan, 69:35, June 12, 1948.
      Smith and Taylor, Bull. U. S. Natl. Mus., 194:85, June 17, 1948;
      Univ. Kansas Sci. Bull., 33:316, March 20, 1950. Stuart, Contr.
      Lab. Vert. Biol., Univ. Michigan, 45:48, May, 1950. Taylor, Univ.
      Kansas Sci. Bull., 35:891, July 1, 1952; Univ. Kansas Sci. Bull.,
      39:25, November 18, 1958.

  _Hyla phlebodes_, Cole and Barbour, Bull. Mus. Comp. Zool., 50:154,
      November, 1906. Kellogg, Bull. U. S. Natl. Mus., 160:172,
      March 31, 1932.

  _Hyla microcephala martini_ Smith, Herpetologica, 7:187, December
      31, 1951 [Holotype.--UIMNH 20965 from Encarnacion, Campeche,
      México; H. M. Smith collector]. Stuart, Contr. Lab. Vert. Biol.,
      Univ. Michigan, 68:46, November, 1954. Fugler and Webb,
      Herpetologica, 13:105, July 10, 1957. Stuart, Contr. Lab. Vert.
      Biol., Univ. Michigan, 75:17, June, 1958. Neill and Allen, Publ.
      Research Div., Ross Allen's Reptile Inst., 2:26, November 10,
      1959. Duellman, Univ. Kansas Publ., Mus. Nat. Hist., 13:62,
      August 16, 1960. Stuart, Herpetologica, 17:74, July 11, 1961.
      Hensley and Smith, Herpetologica, 18:70, April 9, 1962. Stuart,
      Misc. Publ. Mus. Zool., Univ. Michigan, 122:36, April 2, 1963.
      Holman and Birkenholz, Herpetologica, 19:144, July 3, 1963.
      Duellman, Univ. Kansas Publ., Mus. Nat. Hist., 15:225, October 4,
      1963; Univ. Kansas Publ., Mus. Nat. Hist., 15:588, June 22, 1965.

  _Hyla microcephala underwoodi_, Smith, Herpetologica, 7:188,
      December 31, 1951.


_Diagnosis._--Brown lateral stripe narrow, extending to groin or
only to sacral region, bordered above by narrow white line; dorsal
pattern bold, consisting of X- or )(-shaped mark in scapular
region or pair of interconnected dark lines on back; interorbital
dark mark usually present; shanks usually having dark transverse
bars.

_Description and Variation._--The dorsal color pattern is highly
variable. The various permutations of the X-shaped scapular mark
and dark sacral marks differ proportionately in different samples.
The variation in color pattern in 12 samples is summarized in
Table 2. In samples from the southern part of the range (southern
Nicaragua and Guanacaste Province, Costa Rica) more (40-93%)
individuals have the lateral stripes extending to the groin than
in northern samples (0-42%) from southern México and Guatemala.
Likewise, the percentage of specimens lacking bars on the shanks and
a dark interorbital bar is higher in the Costa Rican samples than
elsewhere in the range. The X- or )(-shaped scapular markings and
/\- or / \-shaped sacral markings are most prevalent in northern
samples, whereas to the south the dorsal markings are more commonly
arranged in a pattern of paired lines, which usually are discontinuous
and usually extend posteriorly only to the sacral region. Thus, the
color pattern in _H. m. underwoodi_ in the southern part of its range
shows trends towards the pattern characteristic of _H. m.
microcephala_. Intergrades between these two subspecies have
been discussed in the account of the nominate subspecies.



  Table 2.--Variation in Color Pattern in Hyla microcephala underwoodi
==========================================================================
  Population        |  N |   Shanks    || Interorbital   || Dorsolateral |
                    |    |             ||     bar        ||   stripe     |
                    |    |-------------||----------------||--------------|
                    |    | Bars |Flecks|| Present| Absent|| Groin| Sacrum|
--------------------------------------------------------------------------
Oaxaca:             | 27 |  22  |   5  ||   27   |   0   ||   0  |   27  |
  Donají-Sarabia    |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Tabasco:            | 55 |  46  |   9  ||   55   |   0   ||   0  |   55  |
  Teapa-Villahermosa|    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Guatemala:          | 51 |  51  |   0  ||   51   |   0   ||  17  |   34  |
  La Libertad       |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Guatemala:          | 32 |  32  |   0  ||   32   |   0   ||   0  |   32  |
  Finca Chamá       |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Guatemala:          | 31 |  31  |   0  ||   31   |   0   ||  14  |   17  |
  Puerto Barrios    |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Honduras:           | 13 |  13  |   0  ||   13   |   0   ||   9  |    4  |
  Lago Yojoa        |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Nicaragua:          | 56 |  44  |  12  ||   54   |   2   ||  13  |   43  |
  La Cumplida       |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Nicaragua:          | 10 |  10  |   0  ||   10   |   0   ||   8  |    2  |
  Tipitapa          |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Nicaragua:          | 10 |  10  |   0  ||   10   |   0   ||   8  |    2  |
  Santo Thomás      |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Costa Rica:         | 12 |   0  |  12  ||    6   |   6   ||   7  |    5  |
  Tenorio-Tilarán   |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Costa Rica:         | 38 | 21[A]|  15  ||   34   |   4   ||  25  |   13  |
  Las Cañas-Liberia |    |      |      ||        |       ||      |       |
                    |    |      |      ||        |       ||      |       |
Costa Rica:         | 32 |  26  |   6  ||   29   |   3   ||  30  |    2  |
  Esparta           |    |      |      ||        |       ||      |       |
--------------------------------------------------------------------------

==========================================================================
  Population        |      Scapular markings     ||       Sacral         |
                    |                            ||      markings        |
                    |----------------------------||----------------------|
                    |   X  |  )(  |  ][  | Other ||  /\  |  / \  | Other |
--------------------------------------------------------------------------
Oaxaca:             |  23  |   4  |   0  |   0   ||   7  |   6  |   14   |
  Donají-Sarabia    |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Tabasco:            |  53  |   2  |   0  |   0   ||  19  |  11  |   23   |
  Teapa-Villahermosa|      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Guatemala:          |  45  |   6  |   0  |   0   ||  16  |  14  |   21   |
  La Libertad       |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Guatemala:          |  32  |   0  |   0  |   0   ||  26  |   2  |    4   |
  Finca Chamá       |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Guatemala:          |  23  |   0  |   4  |   4   ||   6  |   4  |   21   |
  Puerto Barrios    |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Honduras:           |   3  |   2  |   3  |   5   ||   2  |   1  |   10   |
  Lago Yojoa        |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Nicaragua:          |  11  |  35  |   8  |   2   ||   0  |  19  |   37   |
  La Cumplida       |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Nicaragua:          |   0  |   5  |   3  |   2   ||   0  |   3  |    7   |
  Tipitapa          |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Nicaragua:          |   3  |   0  |   7  |   0   ||   0  |   5  |    5   |
  Santo Thomás      |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Costa Rica:         |   0  |   0  |  12  |   0   ||   0  |   0  |   12   |
  Tenorio-Tilarán   |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Costa Rica:         |   0  |  11  |  19  |   8   ||   0  |   0  |   38   |
  Las Cañas-Liberia |      |      |      |       ||      |      |        |
                    |      |      |      |       ||      |      |        |
Costa Rica:         |   0  |   0  |  14  |  18   ||   0  |   0  |   32   |
  Esparta           |      |      |      |       ||      |      |        |
--------------------------------------------------------------------------

[Footnote A: Longitudinal stripes present in two specimens.]



When this frog is active at night its dorsum is pale yellow; faint
flecks are present in some individuals. The white dorsolateral line
usually is evident in the tympanic region, but in many individuals a
dorsal pattern of lines and other marks is not evident. By day the
dorsum changes to yellowish tan or pale brown with dark brown or
reddish brown markings (Pl. 13). The venter is white, and the vocal
sac in breeding males is yellow. The iris is pale bronze with a brown
tint anterior and posterior to the pupil.

_Remarks._--_Hyla microcephala underwoodi_ has had a confused
nomenclatural history. The taxon was first named _Hyla microcephala_
by Boulenger (1898); this name was preoccupied by _Hyla microcephala_
Cope (1886). Cole and Barbour (1906) and Kellogg (1932) used the name
_Hyla phlebodes_ Stejneger (1906) for specimens of this frog from
México. Dunn (1931, 1933, 1934) applied the name _Hyla underwoodi_ to
Panamanian specimens that we identify as _Hyla phlebodes_. Smith
(1951) named _Hyla microcephala martini_ from southern México and
Guatemala and considered the northern populations to represent a
subspecies distinct from the Costa Rican _Hyla microcephala
underwoodi_, despite the fact the Stuart (1935:39) stated that
comparisons of specimens from El Petén, Guatemala, with the holotype
of _Hyla underwoodi_ showed only trivial differences.

Much of the confusion regarding the name _Hyla underwoodi_ stems from
the illustration given by Boulenger (1898:pl. 39, fig. 3) and
reproduced by Taylor (1952:892), which shows a frog having a unicolor
dorsum, dorsolateral white lines, and dark flanks. This pattern is in
marked contrast to the pattern seen in most preserved specimens, which
have the dorsum variously marked by dark brown lines or irregular
marks. Smith (1951:185), in his description of _Hyla microcephala
martini_ from southern México, considered _H. underwoodi_ to be a
subspecies of _H. microcephala_ that lacked dorsal dark markings.

Data accumulated in 1961 through field studies by the senior author at
the type locality, Bebedero, and other localities in Guanacaste and
Puntarenas provinces in Costa Rica provide a reasonable explanation of
the differences in color pattern. As noted in the preceding description
of this subspecies, at night the dorsal markings are not evident in
many living individuals, whereas by day the dorsal markings are
prominent. Most collectors prepare their specimens by day; consequently
the majority of specimens have a pronounced dorsal pattern. Of the
frogs collected in Costa Rica in 1961, some specimens were preserved
at night; others from the same series were preserved by day. The
differences are striking. In those preserved at night, dorsal markings
are faint, if present at all. Some specimens closely match the figure
given by Boulenger (1898).

It is extremely doubtful if the frog described and illustrated by
Boulenger could be associated with either _Hyla phlebodes_ or _H.
microcephala microcephala_. Individuals of the former species lack
a dorsolateral white line and always have some dorsal markings
evident at night; furthermore, _H. phlebodes_ is not known to occur
on the Pacific lowlands. _Hyla microcephala microcephala_ occurs
farther southeast. Since there is no reason to doubt the type locality
of _H. underwoodi_, since specimens from the area around the type
locality that have been preserved at night are like the holotype in
pattern, and since the characteristics of the populations of the frogs
in Guanacaste are the same as, or gradually blend into those of,
populations in northern Central America and southern México, the
frogs from throughout the entire range can be referred to one taxon,
the earliest name for which is _Hyla underwoodi_ Boulenger, which
herein is considered to be a subspecies of _H. microcephala_ Cope.

_Distribution._--_Hyla microcephala underwoodi_ inhabits the
Atlantic slopes and lowlands from southern Veracruz and extreme
northern Oaxaca eastward across the base of the Yucatan Peninsula
(possibly the species is extant in the northern part of the
peninsula) to British Honduras and thence southeastward through
the Caribbean lowlands and interior valleys in Honduras to central
Nicaragua, where it apparently avoids the forested Caribbean
lowlands and the dry Pacific lowlands of northwestern Nicaragua,
but in the vicinity of Managua invades the Pacific lowlands and
continues southward into northwestern Costa Rica as far as the
Puntarenas Peninsula (Fig. 1). In México and Guatemala the species
has not been taken at elevations of more than 350 meters, whereas
farther south it occurs at higher elevations--780 meters at
Silencio, Costa Rica, 830 meters on Montaña de Guaimaca, Honduras,
960 meters at Finca Tepeyac, Nicaragua, and 1200 meters at Finca
Venecia, Nicaragua.

_Specimens examined._--1270, as follows: +Mexico+: Campeche: Balchacaj,
FMNH 100406, UIMNH 20944-6; Encarnación, FMNH 27069-70, 75784,
MCZ 28360, 29637, UIMNH 20948-58, 20965, USNM 134264-5; Escárcega,
UMMZ 122999; *7.5 km. W Escárcega, KU 71229-43; Laguna Alvarado, 65 km.
S Xpujil, KU 75084-9; Pacaitún, Río Candelaria, FMNH 83118-20;
*Tres Brazos, FMNH 113101-22, UIMNH 20947; 10 km. W Xpujil, KU 75082-3.
Chiapas: Palenque, UIMNH 47984, 49139-50, USNM 114973-8. Oaxaca: *5 km.
N Chiltepec, KU 87015-23; 3 km. N Donají UMMZ 115249 (9); *3.7 km.
N Donají, UMMZ 115250 (5); *43 km. N Matías Romero, UIMNH 42550-68;
*3.5 km. N Palomares, TNHC 25185, 25321-31, 25341-68; 4.6 km. N
Sarabia, UMMZ 115247 (2); *6.1 km. N Sarabia, UMMZ 115248 (11), *3 km.
N Tolocita, KU 39655; Tuxtepec, KU 87024-40. Tabasco: 24 km. N
Frontera, MCZ 35665-70; 0.8 km. E Río Tonolá, TNHC 25189; Teapa, UMMZ
119218 (4); *2.7 km. N Teapa, UMMZ 119216 (4); *10 km. N Teapa, UMMZ
119217 (6); *11.5 km. N Teapa, UMMZ 119219; *15.2 km. N Teapa, UMMZ
119220 (4); *17.6 km. N Teapa, UMMZ 119221 (12), 3.3 km. S Villahermosa,
UMMZ 119215 (12), *17.6 km. S Villahermosa, UMMZ 119214 (12).
Veracruz: 2.1 km. N Acayucan, UIMNH 42547-9; *6.4 km. NW Acayucan,
UMMZ 115254 (14); 1.6 km. ESE Alvarado, UMMZ 115258 (39); *2.4 km. ESE
Alvarado, UMMZ 115251 (2); *4.5 km. S Aquilera, UMMZ 115252 (21);
*8 km. SW Coatzacoalcos, UMMZ 119213 (10); 2.2 km. E Cosoleacaque,
UMMZ 119222 (26); 10 km. SE Hueyapan, UMMZ 115255; 0.8 km. S Lerdo de
Tejada, UMMZ 122778; *3.6 km. NE Minatítlán, TNHC 25150-2; 1.9 km. S
Naranja, UMMZ 115253 (3); 4.5 km. NE Novillero, UMMZ 115256; San Andrés
Tuxtla, FMNH 113124-8, UIMNH 20942-3. Yucatán: Chichén-Itzá, FMNH 36570,
MCZ 2463 (2).

+British Honduras+: Cayo: 6.2 km. S El Cayo, MCZ 37885-92. Stann Creek:
Stann Creek, FMNH 49068.

+Guatemala+: Alta Verapaz: 28.3 km. N Campur, KU 64578-90; Chinajá,
KU 57425; Cubilquitz, UMMZ 90887, 90888 (4); Finca Chamá, UMMZ 90879
(13), 90880 (4), 90881, 90882 (28), 90883 (12), 90884 (46), 90885 (39),
90886 (20); *Finca Tinaja, BYU 16032; Panzós, UMMZ 90889 (2).
Chiquimula: Chiquimula, UMMZ 98113; 2 km. N Esquipulas, UMMZ 106844.
El petén: La Libertad, KU 57447-97, 59907-11 (skeletons), MCZ 21461,
UMMZ 75332 (13), 75333 (11), 75334 (14), 75335 (10); Piedras Negras,
FMNH 113123, UIMNH 20966; *5 km. S Piedras Negras, USNM 114951-72;
Tikal, UMMZ 117981 (2); Toocog, 15 km. SE La Libertad, KU 57426-46. El
Quiché: Finca Tesoro, UMMZ 89165 (5). Huehuetenango: Finca San Rafael,
16 km. SE Barillas, FMNH 40917-9. Izabal: Puerto Barrios, FMNH
20004-7; 8 km. S Puerto Barrios, KU 57507-37, 59991 (eggs), 59992
(tadpoles); Quirigua, CAS 69657-701; 2.5 km. NE Río Blanco, KU 57539;
San Felípe, FMNH 35065. Zacapa: 14 km. ENE Mayuelas, KU 57502-6; 8 km.
ENE Río Hondo, KU 57498-501.

+Honduras+: Atlantidad: La Ceiba, UMMZ 91948 (2), USNM 117593-600;
Lancetilla, MCZ 17981. Cortes: Lago Yojoa, AMNH 54917-9, 54957, 55134,
KU 64563-77. El Paraiso: Valle de Jamastran, AMNH 54807-12.
Francisco-Moranza: El Zamorano, AMNH 54873-81, KU 103223, UMMZ 123101;
Montaña de Guaimaca, AMNH 54900-4 (8); Ranch San Diego, 19 km. SW
Guaimaca, AMNH 53939. Itibucá: Vieja Itibucá, AMNH 54912-3.

+Nicaragua+: Chontales: 3 km. SW Santo Tomás, KU 64770-9, 68308
(skeleton). Esteli: Finca Venecia, 7 km. N, 16 km. E Condega, KU
85296; 2.4 km. N Estelí, MCZ 28933-7. MANAGUA: 12-13 km. E Managua,
KU 85297-301; *10 km. SW Tipitapa, UMMZ 119977 (10). Matagalpa: *Finca
Tepeyac, 10.5 km. N, 9 km. E Matagalpa, KU 85302-3; Hacienda La
Cumplida, KU 64780-96, 68309-11 (skeletons), UMMZ 116482 (8), 116483
(23), 116484 (3), 116485 (5), 119984 (3). Rivas: *Finca Amayo, 13 km.
S, 14 km. E Rivas, KU 85304-7; 16 km. S Rivas, MCZ 29011-7; *20.5 km.
SE Rivas, KU 85308-10; 5 km. SE San Pablo, KU 43111-4.

+Costa Rica+: Guanacaste: Arenal, USC 6254 (2); *3 km. W Bagaces, USC
7019 (10); *3 km. NE Boca del Barranca, USC 8017 (21), *Finca San
Bosco, USC 6272 (6), 6276 (3); *Guayabo de Bagaces, USC 7022 (4), 7023
(3), 7025; 12 km. S La Cruz, USC 8091 (2); *Laguna Arenal, USC 6262;
*27 km. N Las Cañas, USC 8171 (6); *16 km. E Las Cañas, KU 102252-8;
16 km. SSE Las Cañas, KU 65090-5; *20 km. SE Las Cañas, KU 102251;
Liberia, KU 30827-39; *7.3 km. N Liberia, USC 8096 (4); *10 km. N
Liberia, USC 8085 (9); *7.5 km. SE Liberia, KU 65102-8, 68621-2
(skeletons); *14.7 km. S Liberia, USC 8238 (3); *4 km. W Liberia, KU
36847-57; 2 km. S Nicoya, USC 8230; *3-10 km. ESE Playa del Coco, USC
8012 (16), 8137 (14); *21.6 km. ESE Playa del Coco, USC 8138 (13);
*Peñas Blancas, KU 102247-50; *Río Bebedero, 5 km. S Bebedero, KU
65089; *Río Higuerón, USC 7168 (2); Santa Cruz, USC 8232 (2);
*Silencio, USC 6248; *Tenorio, KU 32313; Tilarán, KU 36858-60; *2 km.
E Tilarán, KU 86403, *5 km. NE Tilarán, KU 36840-6 USC 6269.
Puntarenas: Barranca, KU 32305-12, *5 km. WNW Barranca, UMMZ 119976
(2); *10 km. E Esparta, KU 86400-2; 1 km. WNW Esparta, KU 65101; *4 km.
WNW Esparta, KU 65088; *10 km. WNW Esparta, KU 65063-87, 68616-20
(skeletons); *12 km. WNW Esparta, KU 65096-100, USC 8251; 21.8 km.
W San Ramón, USC 8242 (15).



+Hyla robertmertensi+ Taylor


  _Hyla robertmertensi_ Taylor, Proc. Biol. Soc. Washington, 50:43,
      April 21, 1937 [Holotype.--CNHM 100096 (formerly EHT-HMS 2270)
      from Tapachula, Chiapas, México; H. M. Smith and E. H. Taylor
      collectors]. Smith and Taylor, Bull. U. S. Natl. Mus., 194:84,
      June 17, 1948; Univ. Kansas Sci. Bull., 33:326, March 20, 1950.
      Mertens. Senckenbergiana, 33:170, June 15, 1952;
      Senckenbergischen Naturf. Gesell., 487:30, December 1, 1952.
      Stuart, Contr. Lab. Vert. Biol., Univ. Michigan, 68:47,
      November, 1954. Duellman, Univ. Kansas Publ., Mus. Nat. Hist.,
      13:63, August 16, 1960. Duellman and Hoyt, Copeia, 1961 (2): 417,
      December 19, 1961. Porter, Herpetologica, 18:168, October 17,
      1962. Stuart, Misc. Publ. Mus. Zool., Univ. Michigan, 122:36,
      April 2, 1963. Duellman and Trueb, Univ. Kansas Publ., Mus. Nat.
      Hist., 17:348, July 14, 1966.


_Diagnosis._--Brown lateral stripe wide, including loreal region and
entire tympanum, extending to groin, bordered above by narrow white
line; dorsum unicolor or with pair of dark lines (or rows of dashes)
usually extending only to the sacral region; shanks having dark flecks,
no transverse bars; interorbital bar lacking.

_Description and Variation._--Males attain a maximum snout-vent length
of 26.4 mm. in Oaxaca, whereas in a sample from Acacoyagua, Chiapas,
the largest male has a snout-vent length of 25.7 mm., and from La
Trinidad, Guatemala, 24-6 mm. Specimens from the western part of the
range (eastern Oaxaca) have slightly smaller heads and proportionately
larger tympani than the more eastern populations (Table 1).

The color pattern shows little variation, except in the nature of the
dorsal markings. In a few specimens from throughout the range, but
especially in the eastern part of the range, the dorsum lacks markings
between the dorsolateral white lines. In most specimens the dorsal
pattern consists of flecks or dashes arranged in two parallel
longitudinal rows, and in some specimens the marks are fused into
parallel lines. Small brown flecks are present on the dorsal surfaces
of the shanks; in some specimens these flecks tend to form a
longitudinal stripe on the shank. An interorbital dark mark is
invariably absent.

When active at night _Hyla robertmertensi_ is pale yellow above with a
white dorsolateral line and pale brown lateral stripe; the dorsal
markings are faint. By day the dorsum is yellowish tan with brown
markings. The dorsolateral stripe is creamy white, and the lateral
stripe is dark brown (Pl. 14). The venter is white, and the iris is
dull bronze. In breeding males the vocal sac is yellow.

_Remarks._--Although this species superficially resembles _Hyla
microcephala microcephala_, the latter is easily distinguished by the
narrow brown lateral stripe, as compared with the much wider stripe
in _H. robertmertensi_. No other hylids in northern Central America
and southern México can be confused with this species.

_Distribution._--_Hyla robertmertensi_ inhabits the Pacific slopes (to
elevations of 700 meters) and lowlands from eastern Oaxaca (east of
the Plains of Tehuantepec) southeastward to central El Salvador. The
species also occurs in the Cintalapa Valley (Atlantic drainage) in
southwestern Chiapas (Fig. 2.) The distribution seems to be limited on
the northwest and southeast by arid environments. The region in which
_Hyla robertmertensi_ lives is characterized by higher rainfall and
more luxuriant vegetation than occur on the Plains of Tehuantepec or
on the Pacific lowlands of eastern El Salvador and southern Honduras.
In addition to the localities listed below, Mertens (1952:30)
recorded the species from Hacienda Cuyan-Cuya, Depto. Sonsonate, El
Salvador.


  [Illustration: Fig. 2. Map showing locality records for
      _Hyla robertmertensi_.]


_Specimens examined._--490, as follows: +Mexico+: Chiapas: Acacoyagua,
USNM 114754-61; *2 km. W Acacoyagua, UMMZ 87843 (28), 87844 (50),
87845 (50), 87846 (45), 87847 (27), 87848 (3); 32 km. N Arriaga, KU
57619-24, 59917-8 (skeletons); Asunción, FMNH 100413, 100501-4, UIMNH
26989-90, USNM 134267; *La Esperanza, USNM 114737-48, 114750-3, 17 km.
S Las Cruces, KU 57625-49, 59997 (eggs); 8.5 km. N Puerto Madero, UMMZ
119981 (2); *11.7 km. N Puerto Madero, UMMZ 119982; Tapachula, FMNH
100096, UIMNH 26987; *11 km. S Tapachula, KU 57605-18, 59916 (skeleton);
Tonolá, FMNH 27073, 100505-10, UIMNH 26988. Oaxaca: Tapanatepec,
UMMZ 115245 (2), *1.6 km. E Tapanatepec, UMMZ 115244 (14); *4.3 km.
E Tapanatepec, UIMNH 38368-9; *7.5 km. W Tapanatepec, UMMZ 115246
(39); 12.8 km. W Tapanatepec, KU 65007-14; 7.2 km. WNW Zanatepec,
UMMZ 115243 (77); *13.6 km. WNW Zanatepec, TNHC 25213-22; 22.7 km.
WNW Zanatepec, TNHC 25203-9.

+Guatemala+: Jutiapa: Jutiapa, UMMZ 106848; La Trinidad, UMMZ
107733 (23). Retalhueleu: Casa Blanca, UMMZ 107732.

+El Salvador+: La Libertad: 16 km. NW Santa Tecla, KU 44112. San
Salvador: 21.9 km. N San Salvador, UMMZ 119983 (6).



+Hyla phlebodes+ Stejneger


  _Hyla phlebodes_ Stejneger, Proc. U. S. Natl. Mus., 30:817, June 4,
      1906 [Holotype.--USNM 2997 from "San Carlos," Costa Rica;
      Burgdorf and Schild collectors]. Taylor, Proc. Biol. Soc.
      Washington, 50:44, April 21, 1937; Univ. Kansas Sci. Bull.,
      35:888, July 1, 1952; Univ. Kansas Sci. Bull., 39:25, November
      18, 1958. Fouquette, Evolution, 14:484, December 16, 1960.
      Duellman and Trueb, Univ. Kansas Publ., Mus. Nat. Hist., 17:348,
      July 14, 1966.

  _Hyla underwoodi_, Dunn, Occas. Papers Boston Soc. Nat. Hist., 5:413,
      October 10, 1931; Occas. Papers Boston Soc. Nat. Hist. 8:72,
      June 7, 1933; Amer. Mus. Novitiates, 747.2, September 17, 1934,
      Gaige, Hartweg, and Stuart, Occas. Papers Mus. Zool., Univ.
      Michigan, 357:5, October 26, 1937. Breder, 1946, Bull. Amer. Mus.
      Nat. Hist., 86:416, August 22, 1946.


_Diagnosis._--Dark brown lateral stripe, if present, usually extending
only to insertion of forearm, never posteriorly to sacral region;
white line above brown stripe absent or faint; dorsal pattern weak,
usually consisting of irregular dashes or interconnected lines;
interorbital dark mark present; shanks having weakly defined
transverse bars.

_Description and variation._--In the majority of specimens (70%) the
lateral dark stripe extends from the nostril to the eye and thence
above the tympanum to a point above the insertion of the arm; in 17
per cent the stripe extends to the mid-flank, whereas in 13 per cent
the stripe is absent. A narrow and faint white line is present on the
canthus in some specimens, but no distinct white stripe is present
above the lateral dark line posterior to the eye. An interorbital bar
and transverse marks on the shanks are invariably present. The dorsal
markings are variable, but in most specimens (92%) consist of either
an X- or )(-shaped mark in the scapular region; in the other specimens
the markings are irregular short lines or absent. Approximately equal
numbers of specimens have a transverse bar, chevron, or broken lines
in the sacral region, whereas about eight per cent of the specimens
lack markings in the sacral region.

When active at night, individuals are pale yellowish tan with faint
brown dorsal markings. By day they are tan with more distinct brown
markings (Pl. 14). The thighs are pale yellow; the belly is white. The
iris is pale creamy tan with brown flecks. In breeding males the vocal
sac is yellow.

_Tadpoles._--Tadpoles of this species have been found in an extensive
grassy pond at Puerto Viejo, Costa Rica. The following description is
based on KU 104099, a specimen in development stage 36 (Gosner, 1960).

Total length, 21.0 mm.; body length, 6.7 mm.; body slightly wider than
deep, snout pointed; nostrils large, directed anteriorly, situated
near end of snout; eyes small, situated dorsolaterally, directed
laterally; spiracle sinistral, located just posteroventral to eye;
anal tube dextral. Tail xiphicercal; caudal musculature moderately
deep, extending far beyond posterior edge of fins; fins deepest at
about midlength; dorsal fin extending onto body, slightly deeper than
caudal musculature; ventral fin slightly shallower than musculature.
Mouth small, terminal, lacking teeth and fringing papillae, but having
finely serrate beaks. In preservative top of head olive-tan with brown
flecks; dark stripe from snout through eye to posterior edge of body;
belly white, flecked with brown anteriorly; tail creamy tan with
grayish brown blotches. In life, dorsum of body reddish tan mottled
with darker brown; lateral stripe dark brown; belly white, mottled
with brown and black; caudal musculature heavily pigmented with
grayish tan; posterior tip of tail marked with dark gray; caudal fins
heavily blotched with grayish tan; iris orange-tan peripherally, red
centrally (Pl. 15).

_Remarks._--This species has been confused with _Hyla microcephala
underwoodi_ by many workers. Dunn (1931, 1933, 1934) and Breder (1946)
referred Panamanian specimens of _H. phlebodes_ to _H. underwoodi_;
likewise, Gaige, Hartweg, and Stuart (1937) made the same error. Cole
and Barbour (1906) and Kellog (1932) used the name _H. phlebodes_ for
Mexican specimens of _H. microcephala underwoodi_. The similarity in
color pattern of _H. microcephala underwoodi_ and _H. phlebodes_
easily accounts for the misapplication of names. Although both species
have nearly identical dorsal color patterns, that of _H. microcephala
underwoodi_ usually is bolder. Furthermore, in that species a narrow
white line usually is present above the well-defined lateral dark
stripe, whereas the lateral dark stripe is short and posterior to the
eye is not bordered above by a white line in _H. phlebodes_.

The type locality "San Carlos, Costa Rica" given by Stejneger
(1906:817) apparently refers to a region, the Llanuras de San Carlos,
in the northern part of Alajuela Province, Costa Rica.


  [Illustration: Fig. 3. Map showing locality records for
      _Hyla phlebodes_.]


_Distribution._--_Hyla phlebodes_ inhabits humid tropical forests from
southeastern Nicaragua southeastward on the Caribbean slopes and
lowlands to the Canal Zone in Panamá, thence eastward in the Chucunaque
Basin of eastern Panamá and onto the Pacific lowlands of Colombia
(Fig. 3). The species also reaches the Pacific slopes in the Arenal
Depression in northwestern Costa Rica and in the Panamanian isthmus,
where it occurs in humid forests on the Pacific slope of El Valle and
Cerro La Campana. Mostly the species is found at low elevations, but
it occurs at 600 meters at Turrialba and at 700 meters at Finca San
Bosco in Costa Rica.

_Specimens examined._--410, as follows: +Nicaragua+: Zelaya: Isla
Grande del Maíz, MCZ 14848; Río Mico, El Recrero, UMMZ 79720 (6).

+Costa Rica+: Alajuela: 12.4 km. N Florencia, MVZ 76108-10, USC 2628;
*Las Playuelas, 11 km. S Los Chiles, USC 7216; Los Chiles, USC 7217,
7219; 3 km. NE Muelle de Arenal, USC 2644 (2); *"San Carlos," USNM
29970. Cartago: Chitaría, KU 103690; *1.6 km. E Río Reventazón Bridge,
east of Turrialba, UMMZ 119978 (2); *Tunnel Camp, near Peralta,
KU 32456, 32458-69, 41098 (skeleton); Turrialba, FMNH 101794, 103188-9,
KU 25725-9, 32439-48, 41095-7 (skeletons), 64797-827, 68300-2
(skeletons), 68403 (eggs), 68404 (tadpoles), MCZ 29224-5, 29310-2,
UMMZ 119979 (6), USC 31, 256 (2), 458 (2), 580, 594, 599 (7), 7074 (2),
USNM 29933. Guanacaste: Arenal, USC 6254; *Finca San Bosco, USC 62724,
6276 (3), Guayabo de Bagaces, USC 7022 (3), 7023; *Laguna Arenal,
USC 6262 (4); 3 km. NE Tilarán, USC 524; *5 km. NE Tilarán, USC 6269;
*6 km. NE Tilarán, UMMZ 122653 (6), S-2680 (skeleton), USC 523 (8).
Heredia: Puerto Viejo, KU 64828-63, 68303-7 (skeletons), 68405-6
(tadpoles), 104099-100 (tadpoles); *1.5 km. N Puerto Viejo, KU 64871;
*1 km. S Puerto Viejo, KU 86432-40; *4.2 km. W Puerto Viejo, KU
64864-5; *5.9 km. W Puerto Viejo, KU 64866-70; *7.5 km. W Puerto Viejo,
KU 86431. Limón: Batán, UMMZ 119980 (2); La Castilla, ANSP 23707;
Puerto +Limón+, KU 32449-55.

+Panama+: Bocas del Toro: 3.2 km. NW Almirante, KU 96026; Cayo de
Agua, KU 96027-31; Fish Creek, KU 96032-4. Canal Zone: Barro Colorado
Island, AMNH 69790, ANSP 23244-50; FMNH 13380, 22972-4; Juan Mina,
AMNH 55429, UU 3899; *8.6-13.8 km. N Miraflores Locks, TNHC 23439,
23477, 23484-8, 23491, 23494-9, 23501-2, 23504-8, 23510-17, 23519-30,
23532-8, 23541-54, 23561. *Rio Chagres, AMNH 55431-4; Río Cocolí,
3.5 km. N Miraflores Locks, TNHC 23461, 23489-90, 23493, 23500, 23503,
23509, 23518, 23531, 23539-40; *Summit, ANSP 23361, KU 97788; *Three
Rivers Plantation, SU 2130. Coclé: El Valle de Antón, AMNH 55435,
69786-9, ANSP 23506-9. Colón: Achiote, KU 77215-78; Ciricito, CAS
71499-500, 71505-6. Darién: Río Canclon at Río Chucunaque, UMMZ 126733;
Río Chucunaque, near Yavisa, AMNH 51783. Panamá: Cero La Campana, FMNH
67847-50.

+Colombia+: Chocó: Andagoya, FMNH 81856; Boca de Raspadura, AMNH
13570-8.



+Hyla sartori+ Smith


  _Hyla underwoodi_ (in part), Smith and Taylor, Bull. U. S. Natl.
        Mus., 194:85, June 17, 1948.

  _Hyla microcephala sartori_ Smith, Herpetologica, 7:186,
      December 31, 1951 [Holotype.--UIMNH 20934 from 1 mile north of
      Organos, south of El Treinte, Guerrero, México; H. M. Smith and
      E. H. Taylor collectors]. Duellman, Univ. Kansas Publ., Mus. Nat.
      Hist., 15:124, December 20, 1961. Porter, Herpetologica, 18:168,
      October 17, 1962. Davis and Dixon, Herpetologica, 20:230,
      January 25, 1965. Duellman, Univ. Kansas Publ. Mus. Nat. Hist.,
      15:652, December 30, 1965.

_Diagnosis._--Dorsum tan with broad dark brown chevrons or transverse
bars; shanks marked with two or three broad transverse bars;
dorsolateral stripes absent.

_Description and variation._--No noticeable geographic variation is
apparent in either structural features or coloration in this species.
All specimens lack a dorsolateral dark stripe and white line, although
a dark line is present on the canthus and dissipates in the loreal
region. A broad interorbital brown bar is present in all specimens.
The color pattern on the dorsum invariably consists of a broad, dark,
chevron-shaped mark in the scapular region and a broad dark chevron or
transverse bar in the sacral region. The shanks invariably have two or
three dark brown transverse bars.

When active at night individuals are yellowish tan above with chocolate
brown markings (Pl. 14). The belly is white, and the thighs are pale
yellowish tan. The iris is dark bronze-color. In breeding males the
vocal sac is yellow. By day some individuals were observed to change
to creamy gray with distinct darker markings.

_Remarks._--Although tadpoles of this species have not been found,
observations on the breeding sites indicate that the tadpoles probably
develop in ponds. Except for calling males observed around a pool in a
stream-bed 11.8 kilometers west-northwest of Tierra Colorada, Guerrero,
all breeding congregations have been found at temporary ponds.

Smith (1951:186) named _Hyla sartori_ as a subspecies of _Hyla
microcephala_. This subspecific relationship seemed reasonable until
analysis of the mating calls showed that the call of _H. sartori_ is
more nearly like that of _H. phlebodes_ than that of _H. microcephala_.
The broad hiatus separating the ranges of _H. microcephala_ and _H.
sartori_ is additional evidence for considering _H. sartori_ as a
distinct species.


  [Illustration: Fig. 4. Map showing locality records for
      _Hyla sartori_.]


_Distribution._--_Hyla sartori_ occurs in mesophytic forests to
elevations of about 300 meters on the Pacific slopes of southern México
from southwestern Jalisco to south-central Oaxaca (Fig. 4). The lack of
specimens from Colima and Michoacán probably reflects inadequate
collecting instead of the absence of the species there. On the basis of
available habitat the species would be expected to occur in Nayarit,
but extensive collecting there has failed to reveal its presence. The
semi-arid Plains of Tehuantepec apparently limit the distribution to
the east.

_Specimens examined._--190, as follows: +México+: Guerrero: 5 km. E
Acapulco, AMNH 54611-2; 23.2 km. N Acapulco, UIMNH 26404-7; Colonia
Buenas Aires, 23 km. E Tecpán de Galeana, UMMZ 119223 (7); *El
Limoncito, FMNH 75785, 100390-402, 104631, 104633, UMMZ 117250, USNM
134266; El Treinte, FMNH 100403, UIMNH 20935-7; Laguna Coyuca, AMNH
59686; La Venta, MCZ 29635; *Morjonares, UIMNH 26392-402; 1.6 km.
N Organos, FMNH 100404-5, UIMNH 20933-4; 19.2 km. S Petaquillas,
UIMNH 26408; 6.1 km. E. Tecpán de Galeana, TNHC 23396-408; *11.2 km.
N Tierra Colorada, UIMNH 26403; 11.8 km. WNW Tierra Colorada, UMMZ
119225 (51), S-2677-9 (skeletons); Zacualpán, UMMZ 119224 (6). Jalisco:
6.4 km. NE La Resolana, KU 67853-69; 24 km NE La Resolana, KU 67870-3.
Oaxaca: 3 km. N Pochutla, KU 57539; 13.4 km. N Pochutla, UMMZ
123495 (40).



CRANIAL OSTEOLOGY


The frogs of the _Hyla microcephala_ group have a minimal amount
of cranial ossification as compared to more generalized hylid skulls,
such as _Smilisca_ (Duellman and Trueb, 1966). In the _Hyla
microcephala_ group the sphenethmoid is small and short, and a large
frontoparietal fontanelle is present. The quadratojugal exists only
as a small spur and is not in contact with the maxillary. The proötics
are poorly developed. The anterior and posterior arms of the squamosal
are short; the anterior arm extends no more than one-fourth of the
distance to the maxillary, and the posterior arm does not have a bony
connection with the proötic. The nasal lacks a maxillary process, and
the medial ramus of the pterygoid lacks a bony connection to the
proötic.

Teeth are absent on the parasphenoid and palatines, but present on the
maxillaries, premaxillaries, and prevomers. The teeth are simple,
pointed, and slightly curved. Although the number of teeth varies
(Table 3), no consistent differences between the species are apparent.


Table 3.--Variation in the Number of Teeth in the Species of the Hyla
      Microcephala Group. (N=Number of Jaws, or Twice the Number of
      Individuals; Means are Given in Parentheses After the Observed
      Ranges).

========================+====+=============+==============+==========
         Species        |  N |  Maxillary  | Premaxillary | Prevomer
------------------------+----+-------------+--------------+----------
_H. microcephala_       | 32 | 31-47(37.8) |  4-13(8.9)   | 2-4(3.2)
                        |    |             |              |
_H. phlebodes_          | 10 | 38-45(40.1) |  8-13(10.3)  | 2-5(3.9)
                        |    |             |              |
_H. robertmertensi_     |  6 | 23-43(32.8) |  7-12(10.5)  | 2-3(2.7)
                        |    |             |              |
_H. sartori_            |  6 | 27-43(38.2) |  9-10(9.3)   | 3-4(3.7)
------------------------+----+-------------+--------------+----------


  [Illustration: PLATE 13
      Upper figure, _Hyla microcephala microcephala_ (KU 64593);
      middle figure, _H. microcephala underwoodi_ (KU 64565);
      lower figure, _H. microcephala underwoodi_ (UMMZ 115247).
      All approximately ×3.]


  [Illustration: PLATE 14
      Upper figure, _Hyla robertmertensi_ (UMMZ 115243);
      middle figure, _H. phlebodes_ (KU 64798); lower figure,
      _H. sartori_ (UMMZ 119225). All approximately ×3.]


  [Illustration: PLATE 15
      Tadpoles of _Hyla microcephala_ group: upper figure, _H. m.
      microcephala_ (KU 104097); lower figure, _H. phlebodes_
      (KU 104099). Both ×4.]


  [Illustration: PLATE 16
      Audiospectrograms and sections of mating calls of _Hyla
      microcephala_ group:
      (a) _H. m. microcephala_ (KU Tape No. 19);
      (b) _H. robertmertensi_ (KU Tape No. 41);
      (c) _H. phlebodes_ (KU Tape No. 6);
      (d) _H. sartori_ (KU Tape No. 190).]


Table 4.--Comparative Cranial Osteology of Hyla microcephala Group

===============+=======================+========================+
   Character   | _H. microcephala_     | _H. robertmertensi_    |
---------------+-----------------------+------------------------+
Frontoparietal | Minimally ossified    | Ossification extensive |
               | with large fontanelle | anteriorly with narrow |
               | extending from        | medial separation;     |
               | sphenethmoid to       | fontanelle largest in  |
               | occipital ridge.      | parietal region.       |
               |                       |                        |
               |                       |                        |
Nasals         | Moderately long and   | Moderate in size;      |
               | slender; arcuate in   | slightly wider         |
               | dorsal view.          | anteriorly than        |
               |                       | posteriorly in dorsal  |
               |                       | view.                  |
               |                       |                        |
Sphenethmoid   | Extremely short in    | Moderately short in    |
               | dorsal view.          | dorsal view.           |
               |                       |                        |
               |                       |                        |
               |                       |                        |
Columella      | Distal and greatly    | Distal and slightly    |
               | expanded.             | expanded or not.       |
---------------+-----------------------+------------------------+
Table 4. (Continued)
===============+========================+========================
    Character  | _H. phlebodes_         | _H. sartori_
---------------+------------------------+------------------------
Frontoparietal | Ossification extensive | Ossification moderately
               | anteriorly with narrow | extensive anteriorly;
               | medial separation;     | medial separation of
               | fontanelle largest in  | about uniform width
               | parietal region.       | throughout length of
               |                        | fontanelle.
               |                        |
Nasals         | Moderate in size;      | Long and broad;
               | slightly wider         | arcuate in dorsal
               | anteriorly than        | view.
               | posteriorly in dorsal  |
               | view.                  |
               |                        |
Sphenethmoid   | Moderately short in    | Moderately short in
               | dorsal view.           | dorsal view; ossified
               |                        | anteriorly between
               |                        | nasals.
               |                        |
Columella      | Distal and not         | Distal and not
               | expanded.              | expanded.
---------------+------------------------+------------------------


  [Illustration: Fig. 5. Dorsal views of the skulls of (a) _Hyla m.
      microcephala_ (KU 68293) and (b) _H. sartori_ (UMMZ S-2677).
      Both × 12.]


  [Illustration: Fig. 6. Dorsal views of skulls of (a) _Hyla phlebodes_
      (KU 68303) and (b) _H. robertmertensi_ (KU 59917). Both × 12.]


Despite the great reduction in the ossification of the cranial
elements, certain apparently consistent differences exist between the
species seem to be consistent. The most notable differences are:
1) amount of ossification of the frontoparietals and consequent shape
and size of the frontoparietal fontanelle, 2) shape of the nasals,
3) shape and extent of the sphenethmoid, and 4) shape of the columella
(Table 4, Figs. 5-6). On the basis of these characters, _Hyla
microcephala_ can be set apart from the other species and characterized
as having a poorly ossified frontoparietal and correspondingly large
frontoparietal fontanelle; long, slender, arcuate nasals; extremely
short sphenethmoid; and expanded distal end of the columella. The other
species in the group (_phlebodes_, _robertmertensi_, and _sartori_)
have more ossification of the frontoparietals, broader nasals, only a
moderately short sphenethmoid, and an unexpanded distal end of the
columella. Among these three species, the skulls of _phlebodes_ and
_robertmertensi_ are most nearly alike, whereas the skull of _sartori_
differs by having a differently shaped frontoparietal fontanelle,
broader nasals, and an ossified anterior extension of the sphenethmoid
between the nasals (compare Fig. 5b with Fig. 6 a-b).

Although all skulls examined belong to breeding adults, the extent of
the ossification of the frontoparietals and the resulting shape of the
frontoparietal fontanelle might be correlated with the age of the frog.
Nevertheless, in the 24 skulls of _Hyla microcephala_ examined, the
frontoparietals are less extensively ossified than in the skulls of the
other species. The trivial differences among the other three species
certainly are suggestive of close relationship, but on the basis of
present knowledge of the evolutionary trends in hylid cranial
osteology, the differences offer little evidence for determining
phylogenetic lineage.



ANALYSIS OF MATING CALLS


Calls of all five taxa were compared in several characteristics, of
which three are deemed most significant systematically. These are
1) the pattern and duration of the notes of a call-group, 2) the
fundamental frequency, and 3) the dominant frequency. Air temperatures
were noted at the time the calls were recorded, but no valid
correlation could be determined between this factor and any of the
parameters of the calls; consequently recordings made at all
temperatures (21-29° C.) were grouped together.

_Pattern and duration of notes._--In all five taxa the basic pattern
consists of a call-group made up of one primary note followed by a
series of shorter secondary notes. In some species the secondary notes
differ from the primary in other characteristics. Both subspecies of
_Hyla microcephala_ have a long, unpaired primary note followed by 0
to 18 (usually about 4) somewhat shorter paired secondary notes. In
calls of _Hyla m. microcephala_ the mean duration of the primary is
0.131 (0.10-0.16) second and that of the secondaries is 0.101
(0.05-0.14) second, whereas in _H. m. underwoodi_ the mean duration of
the primary is 0.018 (0.05-0.15) second and that of the secondaries is
0.086 (0.06-0.11) second.

_Hyla robertmertensi_ has a reverse of this pattern in that the primary
note is paired and the secondaries are unpaired. In the sample studied
a call-group contains 0-28 secondary notes (generally about 3). The
mean duration of the primary is 0.091 (0.07-0.11) second and that of
the secondaries is 0.040 (0.025-0.06) second.

_Hyla phlebodes_ and _sartori_ have call-groups composed of a rather
short, unpaired primary and several short, unpaired secondaries
(0-28 in _phlebodes_, 0-23 in _sartori_). The mean duration of the
primary of _phlebodes_ is 0.105 (0.07-0.16) second and that of the
secondaries is 0.067 (0.035-0.12) second. The mean duration of the
primary of _sartori_ is 0.080 (0.07-0.09) second and that of the
secondaries is 0.053 (0.035-0.07) second.

The two subspecies of _H. microcephala_ are identical in call pattern
and agree closely in duration of notes, although those of the nominate
subspecies tend to be slightly longer. _Hyla robertmertensi_ is
distinctive in call pattern in that it is the only species having a
paired primary; the duration of the primary is completely overlapped by
that in the other species, but the secondaries tend to be the shortest
in the group. The call patterns of _H. phlebodes_ and _H. sartori_ are
identical and the range of duration of notes of _phlebodes_ completely
overlaps that of _sartori_, although both the primary and secondary
notes of the latter tend to be somewhat shorter (Table 5, Pl. 16).

_Fundamental frequency._--This parameter was analyzed for the primary
notes. It was measured for the secondaries as well and was found to
differ in magnitude in the same way as the primary note. In a few
examples of both subspecies of _H. microcephala_ a high primary note,
in which the fundamental frequency is exceptionally high, is sometimes
emitted (Fouquette, 1960b). None of these notes was used in this
analysis; only the fundamental frequencies of normal primary notes are
compared (Table 5, Fig. 7).


Table 5.--Comparison of Normal Mating Calls in the Hyla microcephala
    Group. (Observed Range Given in Parentheses Below Mean;
    Unless Otherwise Noted Data Are for Primary Notes.).

----------------+--+---------+---------+-------------------+--------------
                |  |Dominant | Funda-  |Duration of notes  |  Repetition
                |  |         |   mental|    (seconds)      |   rate of
     Species    |N |frequency|frequency+---------+---------+ secondaries
                |  | (cps)   |  (cps)  | Primary |Secondary|(notes/minute)
----------------+--+---------+---------+---------+---------+--------------
_H. m.          |44|   5637  |   205   |   0.13  |   0.10  |    268
  microcephala_ |  |(5150    |(184-244)|(0.11    |(0.05    | (192-353)
                |  |   -5962)|         |   -0.16)|   -0.14)|
                |  |         |         |         |         |
_H. m.          |47|   5772  |   220   |   0.11  |   0.09  |    283
  underwoodi_   |  |(5177    |(192-275)|(0.05    |(0.06    | (197-384)
                |  |   -6200)|         |   -0.15)|   -0.11)|
                |  |         |         |         |         |
_H.             |25|   5388  |   162   |   0.09  |   0.04  |    418
 robertmertensi_|  |(5150    |(140-178)|(0.07    |(0.03    | (368-570)
                |  |   -5785)|         |   -0.11)|   -0.06)|
                |  |         |         |         |         |
_H. phlebodes_  |34|   3578  |   148   |   0.11  |   0.07  |    284
                |  |(3220    |(125-158)|(0.07    |(0.04    | (210-350)
                |  |   -4067)|         |   -0.16)|   -0.12)|
                |  |         |         |         |         |
_H. sartori_    |10|   3217  |   126   |   0.08  |   0.05  |    434
                |  |(2950    |(116-135)|(0.07    |(0.04    | (396-477)
                |  |   -3600)|         |   -0.09)|   -0.07)|
----------------+--+---------+---------+---------+---------+--------------


The two subspecies of _H. microcephala_ agree closely in fundamental
frequency. There is considerable overlap, but the difference
between the means is significant at the 0.001 level of probability
(t = 4.2406). The call of _H. robertmertensi_ does not overlap that
of _H. sartori_ or either subspecies of _H. microcephala_ in this
parameter; but it does overlap that of _H. phlebodes_, although again
the difference between the means is significant at the 0.001 level
(t = 9.360). _Hyla phlebodes_ and _sartori_ have the lowest fundamental
frequencies, and there is some overlap, but here too the difference
between the means is significant at the 0.001 level (t = 4.923).

_Dominant frequency._--A dominant band of frequencies cuts across
the harmonics of the fundamental, obscuring the harmonic pattern and
generally shifting upward in frequency. The midpoint of this band is
measured at the terminal border as the dominant frequency. As with the
fundamental frequency, only the normal primary notes were utilized in
the comparisons (Table 5, Fig 8).


  [Illustration: Fig. 7. Variation in the fundamental frequency of the
      normal primary notes in the _Hyla microcephala_ group. The
      horizontal lines = range of variation, vertical lines = mean,
      solid bars = twice the standard error of the mean, and open
      bars = one standard deviation. The number of specimens in each
      sample is indicated in parentheses after the name of the taxon.]


The two subspecies of _H. microcephala_ agree more closely in this
parameter than in fundamental frequency. The overlap is great, but the
difference between the means is significant at the 0.001 level
(t = 3.658). The calls of both subspecies completely overlap that of
_robertmertensi_ in this parameter, but the difference between the
means is significant at the 0.001 level. The calls of _H. phlebodes_
and _H. sartori_ overlap considerably in this characteristic, although
the difference between the means is significant at the 0.001 level
(t = 7.504) (Fig. 9). The call of neither species overlaps those of
_H. microcephala_ and _robertmertensi_.


  [Illustration: Fig. 8. Variation in the mid-point of the dominant
      frequency band of the normal primary notes in the _Hyla
      microcephala_ group. The horizontal lines = range of variation,
      vertical lines = mean, solid bars = twice the standard error of
      the mean, and open bars = one standard deviation. The number of
      specimens in each sample is indicated in parentheses after the
      name of the taxon.]


  [Illustration: Fig. 9. Scatter diagram relating the dominant and
      fundamental frequencies of the normal primary notes in the
      _Hyla microcephala_ group. Each symbol represents a different
      individual.]


_Repetition rate._--The repetition rate of the secondary notes, in
calls consisting of more than one secondary, was measured for each
form. A considerable amount of variation in this parameter was found
in all of the taxa (Table 5). This variation probably is due in part
to the effect of temperature differences. Repetition rate is the only
parameter analyzed for which there is a correlation with the
air-temperature, but even here the correlation is weak, probably due
to the microenvironmental effects of humidity, air-movement, and other
factors in addition to the ambient air temperature that influences the
body temperature of the frogs. These rates are nearly alike in both
subspecies of _H. microcephala_ and in _phlebodes_. The repetition
rates in _H. robertmertensi_ and _H. sartori_ are considerably faster
than in the other three taxa. _Hyla sartori_ has the fastest
repetition rate of the group.

In all characteristics of the mating calls the two subspecies of
_H. microcephala_ agree closely, as might be expected, although the
differences are statistically significant. _Hyla robertmertensi_ is
distinctive in call pattern and seems to be closer to _microcephala_
in dominant frequency but closer to _H. phlebodes_ in fundamental
frequency. Thus, it is somewhat intermediate between _microcephala_
and _phlebodes_. The identical pattern and similarity in fundamental
and dominant frequencies of the calls of _H. phlebodes_ and _H. sartori_
possibly indicate close relationship.

_Geographic variation in call._--_Hyla m. microcephala_ has higher
fundamental and dominant frequencies in Costa Rica than in Panamá. In
Costa Rican _H. m. underwoodi_ the fundamental and dominant frequencies
are lower than in other parts of the range. Frogs of this subspecies
recorded in Nicaragua and Honduras have slightly lower dominant
frequencies and higher fundamental frequencies than those recorded in
Guatemala or Oaxaca. The duration of both primary and secondary notes
decreases to the south; samples from Nicaragua and Costa Rica have the
shortest notes. Comparison of duration of notes in the two subspecies
shows that the Panamanian _H. m. microcephala_ have slightly longer
notes than do any _H. m. underwoodi_; the more northern populations of
_H. m. underwoodi_ from México most closely approach _H. m.
microcephala_ in this characteristic.

The calls of _H. robertmertensi_ in Oaxaca have higher dominant and
fundamental frequencies and longer secondary notes than do those in
Chiapas.

The calls of _H. phlebodes_ recorded at Puerto Viejo, Costa Rica,
have slightly lower dominant frequencies than do those recorded at
Turrialba, Costa Rica, and in Panamá, whereas those recorded at
Turrialba have lower fundamental frequencies than in other samples.
The duration of notes is slightly shorter in both Costa Rican samples
than in those recorded in Panamá.



LIFE HISTORY


The frogs of the _Hyla microcephala_ group breed in shallow grassy
ponds. In some places they breed in permanent ponds, but usually
congregate around temporary pools, such as depressions in forests,
flooded fields, and roadside ditches. At the height of their breeding
season, usually in the early part of the rainy season, the
congregations are made up of large numbers of individuals. In April,
1961, and in June, 1966, the senior author noted nearly continuous
choruses of _H. m. microcephala_ in roadside ditches along the 75
kilometers of road between Villa Neily and Palmar Sur, Puntarenas
Province, Cost Rica; on June 20, 1966, at Puerto Viejo, Heredia
Province, Costa Rica, he estimated approximately 900 _Hyla phlebodes_
in one pond, and two nights later noticed that the number of
individuals had increased substantially. Other observations by the
first author on size of breeding congregations include nearly
continuous choruses of _H. m. underwoodi_ between Villahermosa and
Teapa, Tabasco, in July of 1958, an estimated 400 _Hyla robertmertensi_
in a road side ditch 7.2 kilometers west-northwest of Zanatepec,
Oaxaca, on July 13, 1956, and approximately 150 _Hyla sartori_ around
a rocky pool in a riverbed, 11.8 kilometers west-northwest of Tierra
Colorada, Guerrero, on June 28, 1958.

The length of the breeding season seemingly is more dependent on
climatic conditions in various parts of Middle America than on
behavioral differences in the various species. Thus, Fouquette (1960b)
found in the Canal Zone that _H. m. microcephala_ formed breeding
choruses from May through January, the entire rainy season in that
area. In the wetter coastal region of Puntarenas Province, Costa Rica,
the species breeds as early as mid-March, whereas in the drier region
encompassing Guanacaste Province, Costa Rica, and southwestern
Nicaragua breeding activity is initiated by the first heavy rains of
the season, usually in June.

_Hyla phlebodes_ inhabits regions having rainfall throughout the year.
Although large breeding congregations are most common in the early
parts of the rainy season, males probably call throughout the year. At
Puerto Viejo in Costa Rica the senior author has heard _Hyla phlebodes_
in February, April, June, July, and August. Charles W. Myers noted
calling males of this species in the area around Almirante, Bocas del
Toro Province, Panamá, in September, October, and February. An
exception to the correlation between rainfall and breeding activity
was noted by the junior author in _Hyla phlebodes_ in the Canal Zone,
where he noticed a decrease in activity of that species in October and
November, when the rains are heaviest and most frequent. Furthermore,
independent observations made by both of us indicate that _H.
phlebodes_ does not reach peaks of activity during or immediately
after heavy rains, but instead builds up to peaks of activity two or
three days after a heavy rain. This is in contrast to the other
species, all of which characteristically inhabit drier environments
than does _H. phlebodes_. Peaks of breeding activity in the other
species occur immediately after, or even during, heavy rains.

The calling location of the males generally is on vegetation above,
or at the edge of, the water. _Hyla microcephala_ and _H. phlebodes_
call almost exclusively from grasses and sedges; _phlebodes_ usually
calls from taller and more dense grasses than does _microcephala_.
Except for some minor differences in calling location observed by
the junior author (Fouquette, 1960b) in the Canal Zone, the differences
in density and height of grasses utilized for calling-locations
probably is dependent primarily on the nature of the available
vegetation. Although bushes and broad-leafed herbs are usually present
at the breeding sites, males of these species seldom utilize them for
calling locations. Both _H. robertmertensi_ and _H. sartori_ have been
observed calling from grasses, herbs, bushes, and low trees. Calling
males of _robertmertensi_ have been found two meters above the ground
in small trees.

Daytime retreats in the breeding season sometimes are no more than
shaded clumps of vegetation adjacent to a pond or in clumps of grass
in a pond. Individuals of _H. m. underwoodi_ were found by day under
the outer sheaths of banana plants next to a water-filled ditch. Dry
season refuges are unknown.

Amplexus is axillary in all four species. Egg deposition has been
observed in _H. m. microcephala_, _m. underwoodi_, and _phlebodes_.
In all three the eggs are deposited in small masses that float near
the surface of the water and usually are at least partly attached to
emergent vegetation. Each clutch does not represent the entire egg
complement of the female.

Tadpoles are definitely known of only _H. m. microcephala_ and
_phlebodes_; these have been described in the preceding accounts of
the species. The tadpoles of these two species can be distinguished
readily (Pl. 15). The tadpole of _H. microcephala_ has a uniformly
white venter and nearly transparent tail, whereas in _H. phlebodes_
the venter is flecked anteriorly and the tail is mottled. In life, _H.
microcephala_ is easily recognized by the orange posterior half of
the tail, whereas the tail in _H. phlebodes_ is mottled tan and grayish
brown.



PHYLOGENETIC RELATIONSHIPS


The evidence already presented on osteology, external structure,
coloration, mating call, and life history emphatically show that the
four species under consideration are a closely related assemblage.
Now the question arises: To what other groups in the genus is the
_Hyla microcephala_ group related? Furthermore, it is pertinent to
this discussion to attempt a reconstruction of the phylogeny of the
group as a whole and of the individual species in the _Hyla
microcephala_ group. With regard to the relationships of the group we
must take into account certain species in South America. Our endeavors
there are hampered by the absence of data on the mating calls and life
histories of most of the relevant species.

As mentioned in the account of _Hyla m. microcephala_, the species
_microcephala_ possibly is subspecifically related to _Hyla misera_, a
frog widespread in the Amazon Basin. _Hyla misera_ resembles
_microcephala_ in coloration, external structure, and cranial
characters. The frontoparietals are equally poorly ossified, and the
frontoparietal fontanelle is extensive. Our principal reason for not
considering the two taxa conspecific at this time is our lack of
knowledge concerning the color of living _H. misera_, the structure of
the tadpoles, and the characteristics of the mating call. Even with the
absence of such data that we think essential to establish the
nomenclature status of the taxa, we are confident that the two are
sufficiently closely related that any discussion of the phylogenetic
relationships of one species certainly must involve consideration of
the other.

_Hyla misera_ possibly is allied to other small yellowish tan South
American _Hyla_ that lack dark pigmentation on the thighs. Probable
relatives are _Hyla elongata_, _minuta_ (with _goughi_, _pallens_,
_suturata_, _velata_, and possibly others as synonyms), _nana_, and
_werneri_. The consideration of the interspecific relationships of
these taxa is beyond the scope of this paper, but we can say that each
of these species has a pale yellowish tan dorsum, relatively broad
dorsolateral brown stripe, and narrow longitudinal brown lines or
irregular marks on the dorsum. Furthermore, examination of the skulls
of _elongata_, _nana_, and _werneri_ reveals that they are like
_misera_ and _microcephala_ in the nature of the frontoparietal
fontanelle and in having a greatly reduced quadratojugal. Thus, on the
basis of cranial and external characters the _Hyla microcephala_ group
can be associated with _Hyla misera_ and its apparent allies in South
America. This association can be only tentative until the mating calls,
tadpoles, and chromosome numbers of the South American species are
known.

Among the Middle American hylids, only the _Hyla microcephala_ group
and _H. ebraccata_ have a haploid number of 15 chromosomes (Duellman
and Cole, 1965). All other New World _Hyla_, for which the number is
known, have a haploid number of 12; the only other _Hyla_ having 15
is a Papuan _Hyla angiana_ (Duellman, 1967).

_Hyla ebraccata_ occurs in the humid tropical lowlands of Middle
America and the Pacific lowlands of northwestern South America. It is
the northernmost, and only Central American, representative of the
_Hyla leucophyllata_ group, which is diverse (about 10 species
currently recognized) and widespread in tropical South America east of
the Andes. This group is characterized by having broad, flat skulls
with larger nasals and more ossification of the frontoparietals than
in the _Hyla microcephala_ group. The quadratojugal is present as a
small anteriorly projecting spur that does not connect with the
maxillary. Externally, the _Hyla leucophyllata_ group is characterized
by having a well-developed axillary membrane, uniformly yellow thighs,
and a dorsal color pattern in many species consisting of a dark lateral
band, a pale dorsolateral band or dorsal ground color, and a large
middorsal dark mark. In some species, the dorsal pattern consists of
small dark markings or is nearly uniformly pale. At least in the
Central American _Hyla ebraccata_, the mating call consists of a
single primary note followed by a series of shorter secondary notes,
the tadpoles have xiphicercal tails and lack teeth, and the haploid
number of chromosomes is 15. On the strength of these observations it
seems imperative to consider the _Hyla leucophyllata_ group as a close
ally to the _Hyla microcephala_ group. Successful artificial
hybridization supports the close relationship of _H. m. microcephala_
and _phlebodes_; partial success of artificial hybridization of these
two with _ebraccata_ (Fouquette, 1960b) provides further evidence for
close relationship between the _Hyla leucophyllata_ and _Hyla
microcephala_ groups.

In México and northern Central America two small species, _Hyla picta_
and _Hyla smithi_, comprise the _Hyla picta_ group. These frogs
resemble members of the _Hyla microcephala_ group by having a
yellowish tan dorsum with a dorsolateral white stripe and uniformly
yellow thighs. Furthermore the mating call is not unlike those of
the species in the _Hyla microcephala_ group. Despite these
similarities, the _Hyla picta_ group differs from the _Hyla
microcephala_ group by having a well-developed quadratojugal that
connects to the maxillary, tadpoles with teeth present and caudal fins
completely enclosing the caudal musculature, and a haploid number of
12 chromosomes. In all of these characteristics the frogs of the

_Hyla picta_ group more closely resemble other Middle American _Hyla_
than they do the _Hyla microcephala_ group. Therefore, it can best be
presumed that the superficial resemblances of coloration and the
mating call are the result of convergence.

Since the _Hyla microcephala_ and _leucophyllata_ groups apparently
are related and since the greatest diversity of these frogs is in
South America (if _Hyla misera_ and its relatives are placed with the
_Hyla microcephala_ group), it seems appropriate to place the centers
of origins of these groups in South America. Therefore, the _Hyla
microcephala_ group and _Hyla ebraccata_ of the _Hyla leucophyllata_
group either have immigrated into Central America, or they are
representatives of those groups that were isolated in Central America
during most of the Cenozoic when South America was separated from
Central America.

The interspecific relationships of the species in the _Hyla
microcephala_ group are not clear. On the basis of coloration, _H. m.
microcephala_ and _H. robertmertensi_ are close, and _H. m. underwoodi_
and _H. phlebodes_ are nearly identical. The mating calls of _H.
phlebodes_ and _sartori_ closely resemble one another, whereas the call
of _robertmertensi_ is intermediate between these and _microcephala_.

In most respects _Hyla microcephala_ is distinct from the other
species, and with the exception of the amount of ossification of the
frontoparietals, the other species can be easily derived from a
_microcephala_-like ancestor. Possibly the slightly increased
ossification of the frontoparietals in _robertmertensi_, _phlebodes_,
and _sartori_ is secondary, or possibly after differentiation of the
species the amount of ossification was further reduced in
_microcephala_. If so, the species fall into a reasonable phylogenetic
scheme that has _microcephala_ as the extant species most like the
ancestral stock.

We visualize the evolutionary history of the group to have followed
a course that began with the invasion of Central America by a
_microcephala_ ancestral stock that differentiated into two populations
in lower Central America--a _microcephala_-like frog on the Pacific
lowlands and a _phlebodes_-like frog on the Caribbean lowlands.
Differentiation could have been brought about by isolation by montaine
or marine barriers. The population on the Pacific lowlands either was
preadapted for subhumid conditions or became so adapted and dispersed
northward onto the Pacific lowlands of northern Central America.
Simultaneously the frogs on the Caribbean lowlands, which were adapted
to humid environments, dispersed northward in the humid forested
regions to southern México and crossed the Isthmus of Tehuantepec onto
the Pacific slopes of Oaxaca and Guerrero northward to Jalisco.
Subsequent development of arid conditions, possibly in the Pliocene,
Pleistocene, or even as late as the Thermal Maximum in post-Wisconsin
time, resulted in a restriction of the ranges in northern Central
America, thereby isolating part of the _phlebodes_-stock on the
Pacific slopes of México, where it adapted to drier conditions and
evolved into _sartori_. The rest of the _phlebodes_-stock was
restricted to the humid forests on the Caribbean lowlands of lower
Central America. The increased aridity on the Pacific lowlands
eliminated the _microcephala_-stock from southern Honduras and
northwestern Nicaragua and in so doing left an isolated population on
the lowlands of Chiapasand Guatemala, which differentiated into
_robertmertensi_. The original stock on the Pacific lowlands of Panamá
and southeastern Costa Rica became _microcephala_.

If the _microcephala_-stock was, as we believe, better adapted for
existence under subhumid conditions than was the _phlebodes_-stock,
the development of subhumid conditions in much of the lowland region
of northern Central America and southern México would have permitted
the expansion of the range of _microcephala_ into the area now
inhabited by _H. m. underwoodi_, while _phlebodes_ was being eliminated
from this area by climatic conditions that were unsuited to its
survival there. Perhaps the similarity in coloration of _H. m.
underwoodi_ and _phlebodes_ is the result of convergence or possibly
hybridization occurred at the time the former was expanding its range
and the latter's range was being restricted. If hybridization did
occur, the differences in mating call subsequently were enhanced,
thereby providing a valid isolating mechanism in sympatric populations.

_Hyla microcephala_ and _phlebodes_ range into northern South America.
Probably both species entered South America in relatively recent times
after they had differentiated from one another in Central America.



LITERATURE CITED


Boulenger, G. A.
  1898. Fourth report on additions to the batrachian collection in the
        Natural-History Museum. Proc. Zool. Soc. London, 1898,
        pp. 373-482, pls. 38-39. October 1.
  1899. Descriptions of new batrachians in the collection of the
        British Museum (Natural History). Ann. Mag. Nat. Hist, ser.
        7, 3:273-277, pls. 11-12.

Breder, C. M. Jr.
  1946. Amphibians and reptiles of the Rio Chucunaque Drainage, Darien,
        Panama, with notes on their life histories and habits. Bull.
        Amer. Mus. Nat. Hist, 86:375-436, pls. 42-60, August 26.

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_Transmitted July 11, 1967._



Transcriber's Notes

This file was derived from scanned images. With the exception of the
list of typographical errors that were corrected below, the original
text is presented.

In the copy of the original, the Plate text contains the notation
"X 2" after the caption to let the reader know that the image was
enlarged by a factor of two.


Emphasis Notation

  _Text_  =  Italic

  +Text+  =  Bold


Typographical Errors Corrected:

Several minor typographical corrections were made (missing periods,
commas, incomplete italicization, etc.); but are not indicated here.
More substantial changes are listed below:

Page 533 - UMZ                    => UMMZ
Page 534 - Diganosis              => Diagnosis
Page 544 - fontanells             => fontanelle
Page 545 - prrimary               => primary
Page 547 - band of of frequencies => band of frequencies
Page 550 - ad                     => had
Page 551 - clumbs                 => clumps
Page 552 - acount                 => account
Page 557 - Minchigan              => Michigan





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