16 U. S. P. R. R. EXP. AND SURVEYS ROUTE IN CALIFORNIA. 



and shining, their posterior margins rounded, the three inferior rows larger than the others ; 

 gastrostiga appearing to a slight extent upon the flanks ; tail short, with a somewhat blunt 

 extremity. 



COLORATION. Milk white above, with thirty-four transverse black bands, including one upon 

 the posterior part of the head ; six complete rings of black upon the tail, and one incomplete 

 just behind the anus ; jaws, chin, throat and abdomen white ; interspaces between rings upon 

 under part of tail white. Abdom. Scuta. 158, Sub. Gaud. 34. 



DIMENSIONS. Length of head, 4 lines ; breadth, 2| lines ; length of body, 9 inch 9 lines ; of 

 tail, 1 inch 7 lines ; total length, 9 inches. 



HABITAT. Mohave Desert. 



GEN. OBS. This serpent resembles no other figured in North America, and is therefore easily 

 recognised. In the genus Sonora of Professors Baird and G-irard, there are, according to them, 

 three postoculars, and two nasal plates on each side with the nostril between them. In Sonora 

 semiannulata there are twenty-five transverse black bands upon the body, and six complete 

 rings upon the tail. The rings in Col. (Zacliolus) zonatus of Blainville, completely surround 

 the body. The nostrils, according to Blainville, open between two plates, but Wagler has 

 them each in a single plate, &quot;in medio scutelli sitis,&quot; in his definition of Zacholus. Wagler, 

 however, cites Col. Riccioli, Metaxa. Serp. Bom. as appearing to belong to this genus, &quot;scheint 

 als Gattung zu gehoren,&quot; but C. Bonaparte represents the nostrils as placed in the commissure 

 between two scuta &quot; gli narici sono situate alia commissura di duo scutelli nasali.&quot;* Blainville 

 represents two half rings upon the head. Zacliolus zonatus is probably allied to Coronella 

 balteata. 



The animal above described approaches very much Simotes in the configuration of the plates 

 upon the head ; but in Simotes the nostrils open between two plates, and the frenal is quite 

 different in shape, being much higher, and not long and slender. The head is also much more 

 robust in Simotes, the body rounded and not flattened, and the tail pointed. The posterior 

 teeth are also longer. The plates upon the upper part of the head are very different from those 

 of Homalosoma, an African genus. The rostral is remarkable, from the fact that so much of it 

 occupies the anterior portion of the upper part of the snout, where, as before remarked, it is 

 triangular in shape, the apex of the triangle passing deeply backward between the internasals. 

 This is also the case in Simotes, and to a greater extent in Rliinosloma ; but in Simotes the snout 

 is conical ; the frontal plate resembles both that of Simotes and Rhinostoma, but is less broad ; 

 the prefrontals and rostral are very different in Rhinostoma, as is also the shape of the body, 

 and the scales in the latter are longer and more hexagonal. Rhinostoma nasicum is a much 

 larger animal. In the specimen in our museum, from Venezuela, which appears to belong to 

 this genus, the nostrils are between two plates, the frenal is more or less quadrangular ; there 

 are two antocular and three postoculars, and the rostral plate is rounded, retroussi, with a 

 sharp and well defined edge. 



1 In Zanunis Rieciola and Zacholus Austriacu.3 of which there are numerous specimens in the Bonaparte collection 

 belonging to the Academy, the nostrils open between two plates. 



