374 SNAKES. 



ClotJio, Severa Ativx, LacJiesis, and Atropos are among their 

 names ; while caudalis and brachyiwa describe the short, thin 

 tail as opposed to the long and tapering tails of most 

 colubrines. The true vipers — those that have not the nasal 

 fosse — belong particularly to Africa, the Crotalidce proper 

 to America, the chief distinction being that the CrotalidcB 

 have and the ViperidcB have not the ' pit ' (see p. 277), of 

 which more in the next chapter. The rigid, lanceolate scales 

 covering the head are another viperine characteristic ; also 

 thick, heavy bodies, tapering at each end, and rough, cari- 

 nated scales. They inhabit for the most part dry, arid 

 deserts and sandy uncultivated places of the Old World, Africa 

 being their most congenial habitat. The coloured viper and 

 young one convey a good idea of their general aspect 



Ophiologists do not agree in the arrangement of genera 

 and species, on account of the forms running so much into 

 each other. Gray gives nine genera and twenty species ; 

 Wallace, three genera and twenty-two species ; and Dumeril, 

 six genera and seventeen species. The Death adder of 

 Australia (p. 172) is a heterogeneous species. Its aspect is 

 viperine, yet it has not viperine fangs, and does not therefore 

 belong to this chapter. Schlegel thinks it ought not to be 

 separated from the true vipers, but Krefft does not state 

 positively that it is viviparous, so it is altogether anomalous. 



The researches of Dr. Weir Mitchel of Philadelphia have 

 been of great value to ophiologists. For two whole years 

 he gave the best portion of his time to the study of rattle- 

 snakes, having a number of them under constant observation. 

 An exhaustive paper by him was published in the SinitJi- 

 sonian Co?itributions, Washington, D.C., in 1860, giving details 



