_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) ------------------------+----+-------------+--------------+----------