206 APPENDIX F. REPTILES. 



2. Crotaphttus collaris, Holbr. 



Spec. char. — Tail conical, very long and tapering; head large, sub- 

 triangular, rounded at the snout ; two subcrescentic black bars, margined 

 with white on each side of the neck ; the largest extends from the origin 

 of the fore-legs to near the dorsal line ; the second of these black bars 

 is smaller, and situated between the latter and the head. 



Syn. — Crotaphytus collaris, Holbr. N. Amer. Herp. II, 1842, "79. 

 PI. x. 



Agama collaris, Say, in Long's Exp. Rocky Mts. II, 1823, 252. — Harl. 

 Med. and Phys. Res. 1835, 142. 



Obs. — The specimens on hand exhibit several varieties of coloration 

 worthy of being noticed : thus two specimens from Gypsum Bluffs, on 

 Red river — a rocky locality — present a green ground-color above, with 

 large blue patches and bright yellow spots; underneath light-green, 

 almost uniform, except under the head, which is deeper and provided 

 with blue, irregularly elongated spots; another specimen from the same 

 locality has brown as the predominating tint. Light-brown stripes are 

 seen on the legs and tail ; similar spots on the body and head ; four 

 rows of red spots on the back; belly light-brown; light reddish-brown 

 under the tail and feet. 



Specimens from the head of the south fork of Red river have either a 

 bluish-gray back, with white spots, a bluish white belly, and the inferior 

 surface of fore-legs reddish, or else the back is yellow and green. 



The above memoranda, on the coloration, were taken on the spot by 

 Capt. Marcy. The general distribution of color appears to indicate sexual 

 differences: thus all the specimens before us in which the spots have a 

 tendency to arrange themselves in transverse bands, or even where 

 transverse narrow bands take the place of the spots, have proved to be 

 females. The ground-color, however, varies in both sexes. 



III. HOLBROOKIA, Girard. 



The genus Holbroohia bears a striking resemblance to the one just 

 described ; it has the same general form, the same sub-triangular head, 

 covered with small polygonal plates, a fold under the throat, small 

 scales on the back, and femoral pores. The tail is perhaps smaller in 

 proportion to the size of the body. The absence of an external auditive 



