POISONOUS AND NON-POISONOUS SNAKES. 99 



sign is uot present the make cannot be a krait, if this is present 

 it mat/ be a krait ; but since a few other snakes and harmless ones 

 share this peculiarity, notably Xenelaphis hexagonotus^ many Dipsas, 

 some AnMycepTialus together with Dendrelaplds and Dendrophis, 

 signs Nos. 2 and 3 must co-exist to clinch the diao'nosis. 



"Vipers — 



Fallacies of methods in common use. [a) The characters frequently 

 taken as a guide to differentiate these snakes and found in many books, 

 vis., triangular head, contracted neck, stout body, and short rapidly 

 attenuating tail, must prove uncertain guides to those unfamiliar with 

 these creatures. It is manifestly impossible for the ordinary man to 

 appreciate what neck is considered contracted, Avhat body stout, and 

 what tail short, unless there are other specimens at hand with contrary 

 peculiarities with which to compare any given specimen ; {b) all these 

 characters may be found either singly or conjointly in other snakes 

 of a harmless kind, so that these guides must be considered as very 

 unsatisfactory. Vipers may be divided into two classes. One of these the 

 Crotalinm, including twelve varieties, is very easy to recognise, be- 

 cause all the species are provided with an opening or pit in the side of 

 the face between the eye and the nostril (see fig. 7). 



These vipers from this peculiarity are called " Pit Vipers." 



The second class, the Viperince or true vipers, includes at least 

 four varieties, of which two are common. They are not quite so easy 

 to distinguish as the last, but may readily be recognised by — 



1. Absence of large scales on the head (see fig. 9, and compare 



with fig. 8). 



2. Ventrals stretching right across the belly (see fig. 11, and 



compare with fig. 12). 



In all the harmless snakes that have no large head scales Eryx, 

 Gongylopliis, etc., when laid on the back, a complete row or more, 

 of scales will be evident on each side of the ventrals simultaneously 

 (see fig. 1 2). 



{N.B. — Xenopeltis is not one of these snakes, and this figure 

 is only given to illustrate this particular point). 



The two vipers that share these peculiarities which concern us at 

 present are Russell's Viper Vipera vel Dahoia russeUii, etc., 

 and the little Indian Viper Echis carinata. 



