ior) 
10. 
ll. 
REPTILES. 
. Parias. Superciliary shield single, hinder labial shields 
smallest; scales lanceolate, of head and body smooth, of crown 
unequal. Asia. 
. Mecw#ra. Superciliary shield double, hinder labial shields 
smallest; scales lanceolate, of head and body smooth. sia. 
. Arropos. Superciliary shields many, forming a prominent 
arched series. Asia. 
b. Subcaudal plates four-rowed at the tip. America. La- 
chesina. 
. Lacuesis. Head ovate; crown scaly. 
. Head more or less shielded. 
c. Subcaudal plates two-rowed ; tail ending in a spine ; cheeks 
not scaly; head-shields with some additional plates in 
front. Trigonocephalina. 
. TRIGONOCEPHALUS. Dorsal scales keeled. 
d. Subcaudal plates one-rowed ; tail ending in a spine ; cheeks 
not scaly ; head shielded. America. Cenchrina. 
. CENCHRIS. 
e. Subcaudal plates one-rowed ; tail ending in a ratile ; cheeks 
scaly ; head more or less shielded. America. Crotalina. 
. CroratopHorvus. Head with nine large shields extending 
behind the eyes. 
Urorsopuus. Head with scales behind; temporal scales and 
labial shield moderate. 
Crotatus. Head with scales behind; temporal scales and la- 
bial shields very small, convex. 
I. Head scaly, with small shields on the edge of the forehead and eye- 
brows ; tail ending in a spine ; cheeks scaly. 
a. Subcaudal plates two-rowed to the tip (Craspedocephalina). 
1. CRASPEDOCEPHALUS. 
Scales lanceolate, keeled: hinder labial shields largest. Con- 
fined to the New World. 
