12 U. S. p. R. R. EXP. AND SURVEYS ROUTE IN CALIFORNIA. 



flexible shell ; the young burst from them into life with the same form they are permanently to 

 retain. There are some, however, among the iioisonous serpents that arc viviparous. So far 

 the true serpents agree in general in their characters and organization, but in some is developed 

 an entirely new set of organs, which invest their possessors with singular and noxious properties. 

 This peculiarity of structure leads to a very natural division of the serpent tribe into two great 

 sections, venomous and non-venomous serpents. 



Venomous serpents are again distributed into different families, according to the arrangement 

 of their fangs, dilatability of jaws, pits about the head, &c., &c. — (Holbrook.) 



I N N c rj I . 



FAMILY I. 



COLUBEID^. 



" Char. 1. The head is covered with plates. 



" Char. 2. The body is much elongated, covered above with scales, and with plates below. 



" Char. 3. The tail is in general long, with bifid plates below, or scutellre, as they are 

 frequently termed. 



" Char. 4. There is no hook near the vent, nor any rudiment of posterior extremities, as in 

 Boa and other non-venomous serpents." 



HERPETODRYAS, Bole. 

 HERPETODRYAS FLAVIGULAEIS, Nob. 



Syn. — Psammophis flavigularis, Hallowell. Proceed. Acad. Nat. Sciences, Oct., 1852. Report 

 of an Expedition down the ZuSi and Colorado rivers, p. 131. 



SlasticojjJiis flavigularis, Baird and Girard. Catalogue of reptiles in Smithsonian institu- 

 tion, p. 98. 



Chin and throat spotted with black ; a black band upon the occiput, and two or three upon 

 the neck, the intervening spaces white ; body yellow with intervening whitish spaces presenting 

 the appearance of fasciie ; 17 rows of scales ; inferior rows larger than the others. 



Dimensions. — Length of head, IJ inch ; breadth, |- ; length of body, 2 feet *l\ inches ; of tail, 

 12 inches. ^ 



Habitat. — California, near the Mohave Desert. 



G-EN. Obs. — The coloration of this animal is somewhat different from that of Psammophis 

 flavigularis, described in Setgreaves' Report, but I do not consider this sufficient to make of it a 

 distinct species. The flagelliformis, according to Bartram, varies much in color, and may possibly 

 be but a variety of this species. The system of dentition differs greatly from that of Psammo- 

 phis, the teeth being all of equal length, whereas, in Psammophis, those near the middle and 

 at the posterior part of the superior maxilla are much longer than the others. The characters 

 of the genus maMicojihis of Professors Baird and Girard are based chiefly upon the form and 

 arrangement of the plates about the head, and are too indefinite, the same arrangement nearly 



