908 16. CROTALIDA 
Genus 48. Crotalus 
Crotalus Linnaeus, Syst. Nat., 10 ed., 1758, Vol. 1, p. 214 (type, Aorridus). 
Crotalophorus Hourruyn, Linn. Nat. Hist., Vol. VI, 1764, p. 290 (same 
type). 
Caudisona Laurent, Syn. Rept., 1768, p. 92 (same type). 
Crotalinus RaFInEsqueE, Am. Month. Mag., Vol. III, 1818 (p. 446), 
Vol. IV, p. 41 (same type). 
Uropsophus Wac.er, Syst. Amph., 1830, p. 176 (type, triseriatus). 
Urocrotalon Firzincer, Syst. Rept., 1843, p. 29 (type, durissus). 
Aploaspis Cope, Proc. Acad. Nat. Sci. Phila., 1861, p. 206 (type, /epida). 
“Echmophrys Cougs, Surv. W. rooth Merid., Vol. V, 1875, p. 609 (type, 
cerastes). 
The head is broad and low, with flattened top, and is very 
distinct from the neck. Its upper surface is covered with 
scales, which are small except sometimes on the snout. The 
anal plate and most or all of the urosteges are undivided. 
The tail is short and ends in a horny rattle or button. The 
dorsal and most of the lateral scales are keeled. 
Synopsis OF SPECIES 
a.—Rostral in contact with anterior nasal. 
b.—Outer edge of supraocular plate normal, not raised 
into a horn-like process. 
c.—Tail entirely black; snout between rostral and supra- 
oculars covered with large plates. 
C. molossus.—p. 911. 
c.—Tail not entirely black; snout not with large plates 
as far back as supraoculars. 
d.—Tail light with black cross-bands; light postocular 
line, if present, reaching row of scales next above 
supralabials anterior to corner of mouth. 
e.—First supralabial usually not divided. General 
coloration grayish or brownish; markings less 
definite, more punctulate; dorsal blotches usually 
not completely surrounded by light margins. 
