The following description of the skull, hyoid, sternum, and prepollex is based on a male specimen of P. spinipollex (KU 68632) that has been cleared and stained. The broad, flat skull (Fig. 3) has a large frontoparietal fontanelle. The ethmoid is large and has a flange laterally. The nasals are of moderate size and in broad contact with the ethmoid, but are separated from one another medially. The anterior half of the maxillary bears a thin, high flange. The anterior process of the squamosal is short and widely separated from the maxillary. The quadratojugal is a small spine-shaped element projecting anteriorly from the ventral base of the quadrate; the quadratojugal does not articulate with the maxillary.
Fig. 3. Dorsal aspect of skull of Ptychohyla spinipollex (KU 68632). Arrow indicates reduced quadratojugal. × 6.
The posteromedian part of the hyoid plate is calcified; from this plate the long bony, posterior cornua (thyrohyales) extend posterolaterally.
The omosternum is calcified, widest anteriorly, and has a convex anterior edge. The calcified xiphisternum is roughly bell-shaped having short lateral processes anteriorly and a deep notch posteriorly.
The swollen thumb is supported by a dorsoventrally flattened spine that does not extrude through the skin.
Variation.—In general, the skull varies little. Usually the quadratojugal is present only as a short element attached to the quadrate, but in one specimen of P. spinipollex the quadratojugal articulates with the maxillary and forms a complete quadratojugal-maxillary arch on each side of the skull. One specimen of P. leonhardschultzei has a complete arch on one side and an incomplete arch on the other.
Only P. spinipollex has lateral processes anteriorly on the xiphisternum; in the other species the xiphisternum is deeply bell-shaped.
Ptychohyla schmidtorum and P. ignicolor have slightly longer premaxillaries than the other species. The longer premaxillary is reflected in the larger number of teeth on the bone—9 to 11 (average 10) in four specimens of P. schmidtorum and 10 teeth in one P. ignicolor, as compared with 6 to 10 (average 7.9) in seven specimens of the other species. The number of maxillary teeth in the various species are: P. euthysanota euthysanota, 43; P. euthysanota macrotympanum, 38; P. leonhardschultzei, 38 and 40; P. spinipollex, 34 and 40; P. schmidtorum schmidtorum, 37 and 43; P. schmidtorum chamulae, 40 and 41; P. ignicolor, 43. The teeth on the premaxillary and anterior part of the maxillary are long, pointed, and terminally curved backwards. Posteriorly on the maxillary the teeth become progressively shorter and blunter.
Variation in number of vomerine teeth is shown in Table 1.
Tadpoles
Tadpoles of the genus Ptychohyla are adapted to live in mountain streams. The bodies are streamlined, and the tails are long and have low fins (Figs. 4 and 5). The mouths are large and directed ventrally. Tadpoles of the two groups of species have strikingly different mouthparts.
Fig. 4. Tadpoles of the Ptychohyla euthysanota group: (A) P. euthysanota euthysanota (KU 60042), (B) P. euthysanota macrotympanum (KU 60049), (C) P. leonhardschultzei (KU 68556), and (D) P. spinipollex (KU 60053). ×2½.
Fig. 5. Tadpoles of (A) Ptychohyla schmidtorum schmidtorum (KU 60051), (B) P. schmidtorum chamulae (KU 58199), and (C) P. ignicolor (KU 71716). × 2½.
Lips of tadpoles of the Ptychohyla euthysanota group (Fig. 6 A-D) are folded laterally; there are 4⁄6 or sometimes 4⁄7 tooth-rows. A lateral "wing" projects on either side of the upper beak. The beaks have blunt, peglike serrations. Lips of tadpoles of the Ptychohyla schmidtorum group (Fig. 6 E-G) are greatly expanded and form a funnel-shaped disc; there are 3⁄3 short tooth-rows. There is no lateral projection or "wing" on either side of the upper beak. The beaks have long, pointed serrations.
Fig. 6. Mouthparts of tadpoles of Ptychohyla: (A) P. euthysanota euthysanota (KU 60042), (B) P. euthysanota macrotympanum (KU 60049), (C) P. leonhardschultzei (KU 68556), (D) P. spinipollex (KU 60053), (E) P. schmidtorum schmidtorum (KU 60051), (F) P. schmidtorum chamulae (KU 58199), and (G) P. ignicolor (KU 71716). × 10.
Variation in certain structural details and in coloration is discussed for each species and subspecies in the systematic accounts that follow. Sizes, proportions, and numbers of tooth-rows are tabulated in Table 2.
Table 2.—Comparison of Certain Larval Characters in the Species of Ptychohyla. (Means Are in Parentheses Below the Ranges.)
| SpeciesNumber of specimensMaximum lengthHead length Total lengthTooth-rowsP. euthysanota euthysanota2340.830.9–37.3 (33.5)4⁄6P. euthysanota macrotympanum1343.330.6–33.4 (32.7)4⁄6P. leonhardschultzei747.529.2–32.7 (31.1)4⁄6P. spinipollex3245.030.2–35.9 (33.0)4⁄7P. schmidtorum schmidtorum1442.528.9–31.2 (29.9)3⁄3P. schmidtorum chamulae445.026.9–29.3 (27.8)3⁄3P. ignicolor239.629.6–29.8 (29.7)3⁄3 |
Evidence on the pattern of development of tooth-rows indicates that the inner rows develop first. A small tadpole of P. euthysanota euthysanota has six lower rows and three fully developed upper rows and only the beginning of the first (outer) upper row. A small tadpole of P. euthysanota macrotympanum has four upper rows and five lower rows. In a small tadpole of P. leonhardschultzei the three upper and four lower tooth-rows are well developed; the first upper and fifth lower rows are beginning to develop, and the sixth lower row is absent. In small tadpoles of P. spinipollex, the sixth lower row is poorly developed, and the seventh row is absent; large individuals normally have seven lower rows. A small tadpole of P. schmidtorum chamulae has 3⁄2 tooth-rows.
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