J 50 Trans. Acad. Sci. of St. Louis. 



Nasal single; anteorbital and loral present. 



Opheodrys. 

 Nasals 2; anteorbital present; loi'al absent. 



Storeria. 

 Nasals 2; anteorbital wanting; loral present. 



Haldea. 

 Four plates between rostral and eye (2 nasals, 1 ante- 

 orbital, 1 loral). Some of the outer rows of scales 

 smooth; scale rows 25-29; ventral plates 200-270. 

 Scale pores present. Elaphe. 



All dorsal scales keeled; scale rows 19-33; ventrals 125-160. 



Natrix. 

 Rostral expanded and shovel-shaped, with a median keel. 



Heterodon. 

 Dorsal scales smooth. 



Loral absent; anteorbital present. Tantilla. 



Loral present; anteorbital absent. 

 Nasal single, pierced by nostril. 



Dorsal rows of scales 13. Carphophis. 



Dorsal rows of scales 19; prefrontals united. 



Farancia. 

 Nasals two, with nostril between them; dorsal scale 

 rows 15-17. Virginia. 



Both loral and anteorbital present. 



Nasals two; anteorbital usually two. 



Adult size large; pairs of subcaudal plates seldom 



fewer than half the number of ventral plates. 



Scale pores present. Bascanion. 



Adult size small; pairs of subcaudal plates seldom 



more than one-third the number of ventral plates. 



BiadopMs. 

 Nasal single; anteorbital single; subcaudals more than 

 one-half the ventral plates. Liopeltis. 



Anal entire. 



Dorsal scales carinated; rostral normal. 



Prefrontals two pairs; scales 25-35 rows. Pituophis. 



Prefrontals one pair; scales 17-21 rows. Nasals divided. 



Thamnophis. 

 Prefrontals a single pair; scales in 19 rows; nasals single. 



Tropidoclonium. 

 Dorsal scales smooth. 



Rostral normal. lampropeltis. 



Family Natricidae. 

 Subfamily Natricinae. 



The Natricinae are without grooved teeth in the posterior part of the 

 upper jaw. (Stejneger.) 



Five genera are known in Missouri. 



