6 BULLETIN 194, UNITED STATES NATIONAL MUSEUM 



Genus SIREN Linnaeus 

 Siren Linnaeus, Systema naturae, ed. 12, vol. 1, pt. 2, 1766, addenda (unpaged). 



Genotype. — Siren tacertina Liimaeus. 



Range. — District of Columbia southward through Florida and west- 

 ward along the Gulf coast to Matamoros, Tamaulipas; north w^ard in 

 the valley of the Mississippi River to Lake Michigan. 



Species. — Three forms, two of them subspecies of S. intermedin, 

 comprise this genus; one enters Mexico. 



SIREN INTERMEDIA NETTINGI Coin 



(Siren intermedia neltingi Goin, Ann. Carnegie Mus., vol. 29, 1942, pp. 211-217. 



Type. — Carnegie Mus. No. 7580. 



Type locality. — Imboden, Lawrence County, Ark. 



Range. — "Southern Louisiana northward to southern Illinois and 

 Indiana, west and south to Maverick Co., Texas, and northern Tamau- 

 lipas, Mexico." Kjiown in Mexico only from Matamoros, Tamau- 

 lipas. 



Suborder Ambystomoidea Noble 



Ambystomoidea Noble, The biology of the Amphibia, 1931, p. 471. 



Family AMBYSTOMIDAE Haliowell 



Anabystomidae Hallowell, Journ. Acad. Nat. Sci. Philadelphia, ser. 2, vol. 3, 

 1858, p. 338. 



KEY TO MEXICAN GENERA OF AMBYSTOMIDAE « 



1. Permanent larva (neotenic) in nature 2 



Normal transformation to adult form (possible exception of Rhyacosiredon 

 zempoalaensis, Amhystoma fluvinaium, and Amhysioma rosaceum) 3 



2. Three phalanges in fourth toe; digits short; the proximal phalanges, at 



least, included in a web; gill branches with filaments to near base; 8 to 10 

 gill rakers on anterior face of third arch; presumably incapable of trans- 

 formation Bathysiredon (p. 7) 



Four phalanges in fourth toe; digits elongate and unwebbed; 12 gill rakers 

 on the anterior face of third arch; capable of artificial transformation, 

 or in case of lerviaensis at least occasionally transformation may take 

 place Siredon (p. 7) 



3. Adults retaining vomerine teeth in a modified larval form; premaxillary 



teeth lost * Rhyacosiredon (p. 8) 



Vomerine teeth arranged with the pterygopalatine teeth to form a trans- 

 verse or slightly arched series near level of choanae; premaxillary teeth 

 retained Ambystoma (p. 10) 



8 The preparation of usable keys to the genera and species of the Ambystomidae is especially difficult 

 owing to the fact that one genus is known only from neotenic larvae, while other genera contain some species 

 known only from adults and others known only from larvae. 



' There is a slight deposition of keratin within the mouth but no horny beak is present, as described by 

 Dunn in the generic description, at any age. 



