10 BULLETIN 194, UNITED STATES NATIONAL MUSEUM 



Genus AMBYSTOMA Tschudi 



Ambystoma Tschudi, M6m. Soc. Sci. Nat. NeuchStel, vol. 2, 1838, p. 92. 

 Sirenodon Desor, Bull. Soc. Sci. Nat. Neuch^tel, vol. 8, 1870, p. 269 (genotype, 



Sirenodon lichenoides Desor = Sir edon lichenoides Ba,iTd=^ Ambystoma tigrinum 



mavortium Baird). 



Genotype. — Ambystoma subviolacea Tschudi= Ambystoma maculatum 

 Shaw. 



Range. — Extreme southeastern Alaska, James Bay, and Labrador 

 southward to the edge of the central plateau in Mexico; apparently 

 not in Baja California. 



Species. — Twenty-eight forms are recognized, 6 of which are sub- 

 species of A. tigrinum; 11 occur in Mexico. 



KEY TO MEXICAN SPECIES OF AMBYSTOMA 

 Known as transformed adults 



1. Small species (maximum known snout-to-vent measurement 62 mm.); 



adpressed limbs separated by three costal folds; vomeropalatine 

 teeth 16-16; maxillary-premaxillary teeth in more than a single series, 

 the outer containing about 40 teeth on each side; tail about 70 percent 



of head-body length schmidti (p. 13) 



Larger species; snout-to-vent measurement exceeding 60 mm 2 



2. Body of adults uniformly colored on dorsal and lateral surfaces 3 



Body not uniformly colored on sides and dorsum 4 



3. Grayish black or plumbeous above and on sides; larvae with three rows 



of small cream spots marking lateral-line system; caudal fin present, 

 in adults, nearly as wide as fleshy part of tail; skin not especially 



smooth ordinarium (p. 13) 



Body of adults uniform grayish brown or lavender-brown, a little lighter 

 below; toes reaching wrist when Umbs are adpressed; tail without 

 distinct dorsal fin, about 75 percent snout-to-vent length; maxillary- 

 premaxillary teeth about 55-55; vomerine teeth 15-17; palatine teeth 

 10-12, the two series separate; skin especially smooth and shining; 

 larvae unknov/n bombypellum (p, 13) 



4. Body uniform blackish above with an irregular row of cream spots 



or an irregular cream stripe low on sides; caudal fin reduced to a 

 fine ridge; adpressed limbs overlap the length of hand; vomeropalatine 

 teeth almost continuous, 31-37 on each side; maxillary-premaxillary 

 series 70-80 on each side; tail about 72 percent of snout-to-vent 



length arablycephalum (p. 13) 



Body not uniformly dark above 5 



