THF. FBIXCIPAL SPECIES OF FOTSOXOT^S SXAKES 67 



(a) Causus. 



(b) Vipera. 



(c) Bifis. 



(d) Cerastes. 



(e) EcJiis. 



(f) At her is. 



(g) Atractaspis. 



(a) Causus. 



(Fig- 35.) 



Head distinct from the neck, covered with symmetrical shields ; 

 nostril between two nasal shields, and the internasal ; eyes 

 moderate, with round pupils, separated from the lips by subocular 

 shields. Body cylindrical ; scales smooth or keeled, oblique on 

 the sides, in 15 — 2'2 rows ; ventral scales rounded. Tail short ; 

 subcaudals in 2 rows or single. 



Four species : — 



(1) C. rliomheatus. — Snout obtuse, moderately prominent. 

 Scales in 17 — 21 rows ; 120 — 155 ventrals ; 15 — 29 subcaudals. 



Colour olive or pale brown, usually with a series of V-shaped 

 brown spots bordered with white, and a large spot in the form 

 of a circumflex accent at the back of the head ; lips bordered with 

 black ; belly yellowish or grey. 



Total length, 700 millimetres ; tail 75. 



Habitat : Tropical and South Africa, from the Gambia to the 

 Cape. 



(2) C. resimus. — -Snout prominent, more or less turned up; 

 scales in 19 — 22 rows ; 134 — 152 ventrals ; 17 — 25 subcaudals. 



Colour greyish-olive on the back ; uniform white on the belly. 

 Total length, 470 millimetres ; tail 40. 

 Habitat : Central and East Africa, Angola. 



(8) C. defilipii. — Snout prominent, more or less turned up. 

 Scales in 17 rows ; 113 — 125 ventrals ; 10 — 18 subcaudals. 



