MEXICAN TAILLESS AMPHIBIANS 17 



KEY TO FAMILIES OF MEXICAN SALIENTIA 



1. Sacral vertebra procoelo us 2 



Sacral vertebra biconvex, with double condyle for coccyx (fig. 

 1, a) ; eighth vertebra biconcave, preceded by seven procoelous 

 vertebrae; without ribs; sacral diapophyses cylindrical or 

 dilated; pectoral girdle firmisternal (fig. 21, p. 195) 6 



2. Sacral vertebra ankylosed to coccyx (fig. 1,6); presacral vertebrae 



eight, uniformly procoelous (rarely opisthocoelous) ; without 

 ribs at any stage in development; sacral diapophyses dilated; 

 pectoral girdle arciferal; pupil of eye vertically elliptical; sole 

 of foot smooth, but provided with a large inner tubercle with 



black cutting edge Pelobatidae (p. 18) 



Sacral vertebrae free (fig. 1, c), with double condyle for coccyx; 

 presacral vertebrae eight to five, procoelous; without ribs; pec- 

 toral girdle arciferal (fig. 3, p . 27) 3 



3. Neither maxillary nor vomerine teeth present; parotoid glands 



generally visible 4 



Maxillary teeth present (except in Engystomops) ; no visible 



parotoid glands; vomerine teeth present or absent 5 



4. Head small and unusually narrowed; no distinct neck; size of 



body disproportionate to size of head; mouth conspicuously 

 small and narrow; snout truncated in front, forming a flat 

 circular disk; eyes rather small; pupil vertical; parotoid glands 

 flattened and not raised above skin on shoulders; no tym- 

 panum; fingers free; toes fully webbed, the tips not dilated; 

 outer metatarsals united; inner toe tuberclelike; a very large 

 shovellike inner metatarsal tubercle; epicoracoid cartilages 

 narrow, scarcelj'^ overlapping; no omosternum; sternum ves- 

 tigial; sacral diapophyses noticeably dilated; terminal phalan- 

 ges simple Rhinophrynidae (Rhinophrynus) (p. 24) 



Head not unusually narrowed; mouth large; parotoid glands 

 distinct; terminal phalanges T-shaped or simple (very rarely 

 claw-shaped); sacral diapophyses cylindrical or dilated; 

 presacral vertebrae eight Buf onidae (p. 27) 



5. No intercalary cartilage or bone between ultimate and penulti- 



mate phalanges of each digit, supporting the claw-shaped or 

 T-shaped terminal joint (fig. 17, p. 76); sacral diapophyses 



cyUndrical or dilated Leptodactylidae (p. 74) 



An intercalary cartilage or bone supporting terminal phalanges 

 (fig. 2), which are generally claw-shaped; sacral diapophyses 

 dilated Hylidae (p. 129) 



6. Head distinctly narrowed and mouth small; generally a fold of 



skin on top of head behind the eyes; a dermal ridge extends 

 across the palate between the choanae, and another in front 

 of the esophagus; tympanum indistinct or not visible; vom- 

 erine teeth absent; sacral diapophyses somewhat dilated; no 



omosternum Brevicipitidae (p. 182) 



Head not unusually narrowed; mouth large; tympanum distinct; 

 maxillary and vomerine teeth present; tongue bicornuate or 

 deeply notched behind; sacral diapophyses cylindrical or 

 slightly dilated Ranidae (p. 189) 



