along the ventrolateral edges of the tarsi and forearms. There are no bright or boldly marked flash-colors (colors that are revealed only when the hind limbs are extended), except in P. ignicolor, which has bright red flash-colors in the groin and on the thighs. In life the iris varies from several different shades of bronze color to deep red in P. schmidtorum schmidtorum.

The degree of metachrosis is moderate. Usually any change of color in life consists only of change in the intensity of color. At times when the over-all coloration is darkened some markings are obscured.

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 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