428 REPTILIA ORDER IILSQUAMATA. 



horns on the head, and by the shields on the lower surface of the tail forming 

 a single instead of a double series. This genus is likewise represented by 

 two desert-haunting species, but one of these has a much wider geographical 

 range than either of the horned vipers, extending from Northern Africa to 

 India, whereas the second is restricted to Palestine and Arabia. Whereas 

 the puff-adder produces a prolonged hissing sound by the expulsion of the 

 air which has been drawn in to blow out the body, the Indian saw- viper 

 gives rise to a somewhat similar sound in a totally different manner. In this 

 species the keels on the scales of the sides of the body are distinctly 

 serrated ; and by rubbing the folds of the body together the contact of these 

 saw-like keels gives rise to a kind of grating, or even hissing noise. This 

 snake is a very fierce species, often attacking without provocation ; and a 

 large percentage of the deaths from snake-bite in India may be attributed to 

 this species and to the equally deadly Russell's viper (Vipera russelli). 



The second sub-family, or OrotdHtUEj the members of which may be col- 

 lectively termed pit-vipers, are typified by the well-known rattle-snakes of 

 the New World, although several other genera belonging to the same sub- 

 family are found in various parts of Asia. There are, however, no representa- 

 tives of this group in Africa, where, on the other hand, the typical vipers, or 

 Viperivwe, attain their maximum degree of development. The distinctive 

 feature of the pit- vipers, and the one from which they take their name, is the 

 presence of a pair of deep pits in the fore front of the head, situated between 

 the eyes and the nostrils in the so-called loreal shields. Doubtless these 

 pits have some special function in the economy of these reptiles, but what this 

 may be naturalists do not seem to have hitherto discovered. The peculiar 

 jointed horny appendage to the tail known as the rattle gives to the snakes 



of the typical genus Crotalus their 

 distinctive name, and at the same 

 time serves to distinguish them 

 at a glance from all the other 

 members of the sub-order. This 

 rattle increases in size by the inter- 

 calation of new joints between its 

 terminal button and the scaly por- 

 tion of the tail, young specimens 

 having only the button. The longer 

 a rattle-snake lives, the more joints 

 it has to its rattle ; and formerly 

 Fig. 27. -A BATTLE-SNAKE (Crotalus). specimens with as many as twenty 



rings were by no means uncommon, 



although at the present day, owing to the war of extermination waged against 

 these noxious reptiles, such are very rare. Very diverse views have been 

 entertained as to the precise use of the rattle to its owner, and since the 

 question is by no means even yet decided, it need not be discussed in this 

 place. All rattle-snakes are characterised by the unusually large size of their 

 venom-glands, and they are consequently among the most deadly of serpents. 

 Most of the eleven representatives of the genus are North American, 

 although one species extends to South America. In their general habits 

 they are very similar to vipers, frequenting dry sandy districts ; but in parts 

 of North America rattle-snakes frequently take up their abode in the warrens 

 of the prairie-marrnot, where they prey on the young of the rightful owners. 

 In the colder parts of their habitat, these snakes become torpid during the 



