VIPERINAE 



639 



with large symmetrical shields, while in the other genera the 

 head-shields are broken up into scales or small shields. Causns 

 rhomheatus is very common in Africa, from the Gambia to the 

 Cape. It reaches a length of a little more than 2 feet. Pale 

 olive-brown above, usually with a dorsal series of large rhombic 

 or V-shaped dark brown, sometimes white-edged spots, and with 

 a dark arrow-shaped mark on the occiput ; under parts yellowish 

 white or grey. 



Bitis s. Echidna. — Very much like Vi^Jera, but the nasal 



Fig. 172. — Bitis aridans (Puff Adder). x 



shields are separated from the rostral by small scales, and the 

 postfrontal bone is very large. Several species in Africa. 



The head is very distinct from the neck, chiefly owing to the 

 large poison-glands and to its being, like the body, much depressed. 

 The small eye has a vertical pupil, and is separated from the 

 labials by a series of small scales. The scales are keeled, and 

 form many, from twenty -nine to forty-one, rows ; the tail is very 

 short, with two rows of scales below. 



In B. aridans, the " Puff Adder," the nostrils are directed 

 upwards. This ugly brute is yellowish to orange brown above 

 with regular, chevron-shaped dark bars or other markings, helping 



