THE PRINCIPAL SPECIES OF POISONOUS SNAKES 49 
In moving over the ground a peculiar sound is produced by the 
friction of its scales. It is capable of springing with great agility 
a fairly long distance on to its prey. When it believes itself in 
danger it coils up, doubling its body twice in the shape of a 
crescent, in the middle of which it places its head, ready to 
strike. Its venom is very rapid in taking effect. 
2.—CROTALIN A. 
(e) Ancistrodon. 
The snakes belonging to this genus of Crotalinæ are found in 
Central and Hastern Asia, but three important species occur in the 
New World, in the United States and Central America. The head 
is covered with nine large symmetrical shields, but the internasals 
and preefrontals are sometimes broken up into scales. The body 
is cylindrical; the tail rather short; the subcaudal scales are 
arranged in one or two rows. 
A. acutus.—The snout of this snake is prolonged into an append- 
age directed forwards. The head-shields are finely granulate. Body 
scales arranged in 21 rows; 162—166 ventrals ; 58—60 subcaudals. 
Coloration brown on the back, with blackish-brown X-shaped 
spots ; head dark brown, yellow on the cheeks, with a black band 
running from the eye to the angle of the jaw; belly yellowish, 
spotted with brown, with a series of large black transverse blotches. 
Total length, 1,500 millimetres ; tail 200. 
Habitat : Upper Yang-tse, China. 
A. halys.—Snout prolonged into an upturned appendage, blunt 
at the tip; 7—8 supralabial scales, the third of which forms part 
of the margin of the eye; body scales in 23 rows; 149—174 
ventrals ; 31—44 subcaudals. 
Coloration yellowish, grey, red, or pale brown above, with darker 
spots or cross-bars. A black spot on the snout; two black spots 
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