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 prootics
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 prootic. The nasal lacks a maxillary process, and
the medial ramus of the pterygoid lacks a bony connection to the
prootic.
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 x3.]
[Illustration: PLATE 14
Upper figure, _Hyla robertmertensi_ (UMMZ 115243);
middle figure, _H. phlebodes_ (KU 64798); lower figure,
_H. sartori_ (UMMZ 119225). All approximately x3.]
[Illustration: PLATE 15
Tadpoles of _Hyla microcephala_ group: upper figure, _H. m.
microcephala_ (KU 104097); lower figure, _H. phlebodes_
(KU 104099). Both x4.]
[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).]