ABT. H. A NEGLECTED GENUS OF SNAKES — DUNN. 3 



Vertebrae: Tretanorhinus and Paraoxyrhopus have hyapophyses 

 on the posterior dorsal vertebrae, and are the only two genera having 

 them which are possible allies of Amastiidium. 



Scalation : Paraoxyrhopus^ Tretanorhinus^ and Hydrocalamus lack 

 scale pits; Thamnodynastes and Diadoyhis have them. My friend, 

 Dr. Frank N. Blanchard, tells me that males of D'tadophis have the 

 scales of the anal region keeled. 



Eye : Thamnodynastes has a vertical pupil. The other genera have 

 a round pupil. 



To sum up : Paraoxyrhopus agrees very closely with Amastridium 

 in all its known characters. The hemipenis, however, is unknown. 



ThamnodyrwsteSy suggested as a related genus by Werner (1903), 

 differs in having a vertical pupil, in having scale pits, and in lacking 

 hypapophyses. 



Hydrocalamus has a different hemipenis, and no hypapophyses. 



Tretanorhinus has a different hemipenis, a very different dentition, 

 and different physiognomy. 



Diadophis has a different hemipenis, different dentition, scale pits, 

 and different phj^siognomy. 



The combination of characters seen in this genus and in its ap- 

 parent allies serves to show {a) the uselessness of the groove on the 

 posterior maxillary teeth as a character of importance; (6) the 

 presence of hypapophyses in American " Opisthoglyph " snakes; (c) 

 the presence of hypapophyses in snakes with forked sulcus spermati- 

 cus. A modification of the present scheme is evidently necessary. 

 I suggest the following as a working basis for determinng the rela- 

 tionships of American Colubrid snakes: 



a\ Sulcus spermaticus divided Dromicinae. 



a'. Sulcus spermaticus single. 



&\ Calyces present. Hypapophyses present-zStbynopftts {"Polyodontophis") . 



b". Calyces present. No hypapophyses GoUihrinae. 



If. No calyces. Hypapophyses present Natricinae. 



