APPENDIX F. REPTILES. 201 



tract as they descend, those of each pair receding slightly from each 

 other, so as to cause the yellow portion to expand about one scale. The 

 black rings are continuous on the abdomen, those of contiguous pairs 

 (not of the same pair) sometimes with their intervening spaces black. 

 The scales in the white rings are always more or less mottled with black, 

 especially along the sides of the body, this mottling being very rarely 

 observable on the red portion. The anterior black ring of the first pair 

 is extended so as to cover the whole head above, except the very tip; 

 the white ring behind it involves the extreme tip of the occipitals. 



A large specimen is much duskier in its colors. The black rings ex- 

 tend on the back so that the contiguous rings of adjacent pairs run into 

 each other. There are 28 pairs of rings, the 25th opposite the anus. 



Dorsal row of scales, 21 ; abdominal ecutellae, 198; subcaudal ones, 

 45. Total length, 20 inches; length of tail, 2f inches. Plate VIII 

 represents the largest of two specimens, caught June 14, near Sweet- 

 water creek. 



VII. MASTICOPHIS, B. & G. 



The prominent feature of this genus consists in a very slender and 

 elongated tail, forming one-third or one-fourth of the length. It bears 

 a close relationship to the black snakes, (JBascanion) from which it dif- 

 fers chiefly in the structure of the plates on the upper jaw. The scales 

 are smooth and disposed in fifteen or seventeen dorsal rows. The pre- 

 anal scutella is divided. The vertical plate is long and narrow. There 

 are two anteorbitals and two postorbitals, these resting against the fifth 

 labial. 



9. Mastic ophis flavigulafjs, B. & G. 



Spec. chae. — Light dull yellow, tinged with brown above. Beneath, 

 two longitudinal series of blotches distinct anteriorly. In alcohol, and 

 especially when the epidermis is removed, the whole animal appears of 

 a soiled white. 



Syn. — Psammophis flavigularis, Hallow. Proc. Acad. Nat. Sc. 



Philad. VI, 1852, 178. 

 Mastkophis jlavigularis, B. & G. Cat. K Amer. Rept. I, 1853, 99. 



Desc. — Size very large. Vertical plate broad before, tapering to the 

 middle, where it is about half as wide as anteriorly, thence it runs nearly 



