840 APPENDIX C. — REPTILES. 



distinct ; the anal ones are wanting. The tail is cylindrical, longer 

 than the body and head together. 



The genus Crotaphytus differs from Holhrookia in having exter- 

 nal auditory apertures, teeth on the pterygoids, and but a minute 

 occipital plate. The shape of the head is likewise more elongated 

 and pointed in front. 



Crotaphytus wislizenii, Baird and Girard. 



Plate III. 

 Spec. chak. — Head proportionally narrow and elongated. Cephalic plates and 

 scales on the back very small. Yellowish brown, spotted all over with small 

 patches of deeper brown or black. 



C. wislizenii has the same general form and appearance as C. 

 coUariSy exhibiting the same contracted neck and fold under the 

 throat, the same compact body, the same cylindrical and elongated 

 tail, and the same shape and proportions of locomotive members 

 and terminating toes. The differences by which the two are dis- 

 tinguished, although of a comparatively minor character, are readi- 

 ly appreciable when both are directly compared. Thus the head 

 of C. wislizenii is proportionally more elongated and narrower than 

 that of 0, collaris. The small and polygonal plates which cover its 

 upper surface and sides are smaller, as well as those of the lip of 

 the lower jaw. The scales of the back are likewise smaller, and 

 those of the belly larger. The tail is somewhat longer, and its 

 scales larger in 0. collaris ; these are subverticillated in both 

 species, and subcarinated from the middle of the back toward its 

 extremity. The pores of the lower surface of the thighs are more 

 conspicuous in C. collaris, independently of the fact that they are 

 generally less so in the female than in the male of the same species. 

 Immediately behind the vent, at the origin of the tail, there exists, 

 in the male, a row of large scales more uniform in C. collaris than 

 in C wislizenii. The specimen figured on our plate III. being a 

 female, these anal plates are not to be seen in fig. 4. 



In the colours of the body distinctive marks will at once be 

 found. (7. collaris possesses on the sides of the neck a double 

 band of black bordered with white, which does not exist in 0. wis- 

 lizenii. The upper surface of the body of the former is scattered 

 all over with small yellow dots, which indeed are found in the lat- 

 ter, but are much smaller and more numerous, having in addition, 

 intermixed with them, irregular roundish brown spots, extending 



