77 



bbb. Both loral atid anteorbital present. 



d. Nasals 2 ; anteorbitals usually 2. 



Adult size large ; pairs of subcaudal plates 



seldom fewer than half the number of ventral 



plates. Bascanion, p. 81. 



Adult size small ; pairs of subcaudal plates 



t seldom more than one-third the number of 



ventral plates. Diadoplm, p. 84. 



dd. Nasal single ; anteorbital single ; subcaudals 



more than one-half the ventrals. 



Cydoplm, p. 85. 

 aa. Dorsal scales more or less keeled.* 



e. Rostral normal ; not shovel-shaped or 



keeled. 



f. Three plates between the rostral and 



the eye. 



Nasal single ; anteorbital and loral 



present. Phyllophilojjhis, p. 86. 



Nasals 2 ; anteorbital present ; loral 



absent. Storeria, p. 88. 



Nasals 2 ; anteorbital wanting ; loral 



present. Haldea. 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, 



A A. Anal plate not divided. 



g. Dorsal scales smooth. 



h. Rostral plate normal. Ophibolus. p. 107, 



hh. Rostral enlarged, trihedral. Cemophora. 



gg. Dorsal scales keeled, rostral normal. 



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



PituopMs. Appendix. 



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



divided. Eutainia. p. 112. 



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



single. Tropidoclonium. Appendix. 



'■' See foot note on preceding page. 



