954 16. CROTALIDJE 



p. 107; MEEK, Field Columbian Mus., Zool. Ser., Vol. VII, No. i, 

 1906, p. 18; DITMARS, Reptile Book, 1907, p. 460, pi. CXXXV; 

 VAN DENBURGH & SLEVIN, Proc. Cal. Acad. Sci., Ser. 4, Vol. 3, 

 1913, p. 429, pis. XXII, XXVIII, fig. i ; ELLIS & HENDERSON, 

 Univ. Colorado Studies, Vol. X, No. 2, 1913, p. 108; ATSATT, Univ. 

 Cal. Publ. Zool., Vol. 12, No. 3, 1913, p. 44; CAMP, Univ. Cal. 

 Publ. Zool., Vol. 12, No. 17, 1916, p. 534; GRINNELL & CAMP, 

 Univ. Cal. Publ. Zool., Vol. 17, No. 10, p. 198; STEJNEGER & BAR- 

 BOUR Check List N. Amer. Amph. Rept., 1917, p. 108; VORHIES, 

 Univ. Ariz. Agric. Exper. Station Bull. No. 83, 1917, p. 360, pi. I, 

 fig. i; STEPHENS. Copeia, 1918, No. 54, p. 35; COWLES, Journ. 

 Entomol. & Zool., Pomona College, Vol. XII, No. 3, 1920, p. 66; 

 STEPHENS, Trans. San Diego Soc. Nat. Hist., Vol. Ill, No. 4, 1921, 

 p. 65; VAN DENBURGH & SLEVIN, Proc. Cal. Acad. Sci., Ser. 4, Vol. 

 XI, 1921, pp. 29, 53; NELSON, Mem. Nat. Acad. Sci., Vol. XVI, 

 1921, pp. 114, 126. 



Caudisona cerastes COPE, in Mitchell's Research. Venom Rattlesn., 

 1861, p. 124; COPE, Proc. Acad. Nat. Sci. Phila., 1866, p. 309; 

 COPE, Proc. Acad. Nat. Sci. Phila., 1867, p. 85. 



McAmofArys cerastes COUES, Surv. W. 100th Merid., Vol. V, 1875, p.609. 



Description. Small. Head rather narrow, flat-topped, 

 varying in outline according to position of fangs, etc. Ros- 

 tral as broad as, or broader than, high, in contact with an- 

 terior nasal. Anterior and posterior nasals usually united, 

 at least above nostril. Usually two preoculars and two inter- 

 nasals. Supraocular very large, raised into a horn-like pro- 

 cess, separated from its fellow by from four to six irregular 

 rows of scales. Eleven to 14 superior and 12 to 14- inferior 

 labials, first pair of latter in contact on median line in front 

 of single pair of genials. Two or three rows of scales be- 

 tween supralabials and eye. Scales in 19 to 25 (usually 21 

 or 23) rowsj feebly keeled except in one to three lower rows 

 on sides, where smooth} those near middle of back with 

 central tubercular swellings. Gastrosteges varying from 134 

 to 150. Urosteges 15 to 25, a few sometimes divided. 



The general color above is gray, often with a yellowish 



