Hurter — Herpetology of Missouri. 151 



Genus natrix. 



Form varying from stout to slender. Head distinct from the body. 

 Crown-shields 9. Loral present. Anteorbitals 1 or 2. Postorbitals 2 or 

 3. Nasals divided with the nostril between. Scales conspicuously 

 keeled; arranged in from 19 to 33 rows. Anal plate divided. (Hay.) 



Key to the Species hst Missouri. 



Scales in 29-31 rows. Numerous narrow cross bands, often broken 

 up. cyclopium. 



Scales in 27 rows. Scales keeled. Brown above with a series of 

 rhomboidal dark spots on the back, which touch with their 

 points. Beneath more or less blotched with black. 



rhombifera. 



Scales in 23-25 rows. Belly with dark spots which are lateral and 

 angular. fasciata. 



Scales in 25 rows. Uniform reddish brown or blackish above red- 

 dish or yellow beneath. fasciata erythrogaster. 



Scales in 23-25 rows. Color in form of brown blotches. Anteorbi- 

 tal one. Upper labials 8. Belly spotted. sipedon. 



Scales in 25 rows. Belly unspotted. Dorsal and lateral rows of 

 blotches alternate to the head. transversa. 



Scales in 19 rows. All scales keeled. A dark vitta on the fourth 

 and eighth dorsal rows. grahamii. 



44. Natrix cyclopium Dumeril and Bibron. Cyclops 

 Water Snake. Green Water Snake. 



Tropidonotus cyclopium, Nerodia cyclopium. 



Description. — Head swollen at the cheeks, narrowed forward. Ros- 

 tral about twice as broad as high. Nasal large, nostril near the upper 

 margin, but not quite dividing it into two plates. Loral large, widest 

 below. One large anteorbital, widest above. Two postorbitals. Two 

 internasals, triangular and about as long as wide. Prefrontals wider 

 than long. Frontal twice as long as wide. Superciliaries much nar- 

 rowed anteriorly. Parietals large. From two to three suborbitals. 

 Upper labials, greatly developed, eight in number; the sixth and seventh 

 much the largest. The sixth twice as long as high. Middle of the eye 

 above the fourth upper labial. Post chin-shields shorter than anterior 

 chin-shields. Six lower labials in contact with the anterior chin-shield. 

 All dorsal scales keeled; those of the outer row slightly, those of the 

 back very strongly, forming sharp longitudinal keels on the tail. Dor- 

 sal rows 27. Ventrals 144. Subcaudals 66 pairs. Anal divided. 



Color. — Color brown above and yellow below. On the upper surface 

 there are on each side two rows of alternating short cross bars of a 

 darker color, which are about one scale wide, and are separated by in- 



