1886.1 ^° [Cope. 



One internasal plate ; no scale-pits Uelicops Wagl. 



Two internasals ; no scale-pits , Amplrfesma D. & B. 



Two internasals ; two scale-pits Bothrodytes* Cope. 



ft Dentition syncranterian or longer behind. 



a. One internasal plate. 

 No scale-pits Atretium\ Cope. 



aa. Two internasal plates. 

 /?. Two nasal plates. 



Anal plate divided ; two scale-pits Tropidonotm\ Kuhl 



Anal plate single ; no scale-pits Eutcenia B. & G 



/?/?. One nasal plate. 



Anal plate single ; rostral produced laterally 8typocemus% Cope. 



Anal plate divided ; rostral normal Amaslridium Cope. 



ftf Dentition isodont, or shorter behind. 



a. Anal plate divided. 



A loreal plate Regina || B. & G. 



No loreal plate Storeria^ B. & G. 



aa. Anal plate entire. 

 (3. Two internasals. 

 Head well distinguished ; a loreal and preocular plates.. AtomarcJius Cope. 

 Head not distinct ; a loreal and a preocular plate. . . Tropidoclonium Cope. 



Head not distinct ; a preocular ; no loreal plate Adelophis Duges. 



A loreal ; no preocular plate Niuia** B. & G. 



A loreal and preoculars ; teeth longer anteriorly Prymnomiodon ('ope. 



/5y9. One internasal plate. 

 Scales keeled ; two nasals and a loreal. 



Haldea\\ B. & G. 

 ** Scales smooth. 



a. Dentition diacranterian. 

 One internasal Liodytes\% Cope. 



aa. Dentition syncranterian. 



One internasal plate ; anals two Limnopliis Gthr. 



Two internasal plates ; anals two P3eudaspin%% Cope. 



aaa. Dentition isodont. 

 Two internasals ; anal entire Ablabes\\ || D. & B. 



*Uen. nov. ; type Amphiesma subminiatum Reitiwt; second species B. tigri- 

 nus = A . tigrinum Boie. 



t Taehynectes Fitz. Cope, Proc. Acad. Phila., 1864, p. 167. Hydrcethiops Gtluth. 

 (nares superior). 



I Nerodia B.&Q. 



§ Chilopoma Cope, preoccupied. 



|| Trelanorhinus D. & B. 



1[ Ischnognathus D. & B. 



** Streptophorus D. & B. 



ft Conocephalus D. & B. 



JJType Helicops alleni Garman. 



gjj Type Coronella cana L. ; D. & B. 



|||| Nalrix Gthr. Neusterophis Gthr. Lycodonomorphus Fitz. sine dlaguosi; nee 

 Ablabes Gthr. et auct., = Rhadincea, etc. 



