77 



bbb. Both loral and anteorbital present. 



d. Nasals 2 ; anteorbitals usually 2. 



Adult size large ; pairs of subcandal platetr 

 seldom fewer than half the number of ventral- 

 plates. Bascanion, p. 81,- 

 Adult size small; pairs of subcaudal plates^ 

 seldom more than one-third the number of 

 ventral plates. Diadophis, p. 84- 

 dd. Nasal single; anteorbital single; subcaudal& 

 more than one-half the ventrals. 



Cyclo2Jhis, p. 85^ 



aa. Dorsal scales more or less keeled.* 



e. Rostral normal; not shovel-shaped or 

 keeled, 

 f. Three plates between the ro&tml andi 

 the eye. 

 Nasal single; anteorbital and loraE 

 present. PhyllophilopMs, p. 86^ 



Nasals 2; anteorbital present; loralJ 

 absent. Storeria, p.. 88- 



Nasals 2 ; anteorbital wanting ; lo^ral 

 present. Ealdea. Appendix, 



ff. Four plates between rostral and eye- 

 (2 nasals, anteorbital, loral). Some- 

 of the outer rows of scales smooth ; 

 rows 25 to 29; ventral plates 200' 

 to 270. Coluber, p. 90.. 



All the scales keeled; rows 19 to» 

 33 ; ventrals 125 to 160. 



Natrix, p. 95.. 

 ee. Rostral expanded and shovel-shaped, with 

 a median keel. Heterodon, p. 102.- 



AA. Anal plate not divided. 



g. Dorsal scales smooth. 



h. Rostral plate normal. Ophibolm. p. 107". 



hh. Rostral enlarged, trihedral. Cemophova. 



gg. Dorsal scales keeled, rogtral normal. 



i. Postfrontals two pairs ; scales in 25 to 35 rows, 



Pitiiophis. Appendix. 



ii. Postfrontals one pair; scales in 17 to 21 rows; nasals 



divided. Eidainia. p. 112. 



iii. Postfrontals a single pair; scales in 19 rows; nasak 



giugle. Tropidodonium. Appendix.- 



''See foot note on preceding page. 



