178 
SNAKES. 
species may be venomous and others innocuous. Many attempts have been made 
to draw up a list of characters by means of which the harmless members of the 
suborder can be distinguished at a glance from those which are hurtful. On this 
point Mr. Boulenger writes “ that there is no sure method of distinguishing the 
two kinds of external characters; except, of course, by a knowledge of the various 
forms. And even then, a cursory examination is not always sufficient, since there 
is, in some cases, a striking resemblance between snakes of totally different affinities, 
by which even specialists may at first be deceived. In short, nothing but an 
examination of the dentition can afford positive information as to the poisonous 
or non-poisonous nature of an unknown snake.” 
Geologically speaking, snakes are a comparatively modern group, 
Distribution. . ® J r J .... 
being scarcely known below the lowest portion of the Eocene division 
of the Tertiary period, although one or two forms have been described from the 
underlying Cretaceous rocks, and one has recently been recorded from the Gault of 
Portugal—a formation underlying the Chalk. It is noteworthy that one of the 
North American lower Eocene snakes has the additional articular facets of the 
vertebrae but very imperfectly developed; and there can be little or no doubt but 
that the whole group is an offshoot from the lizards. From the commencement of 
the Tertiary period, the group seems to have gone on steadily increasing in 
numbers; and it is now represented by some fifteen hundred species, ranging all 
over the world except New Zealand. Snakes are, however, much more abundant 
in the moist tropical regions of the globe than in colder regions, and it is there only 
that they attain their maximum development in point of size. India and the 
Malayan countries, where there are representatives of the whole of the nine families 
into which the suborder is divided, are the home of a greater number of both 
genera and species of snakes than any other part of the world, Tree-snakes are 
very common in this region; while the gigantic pythons are shared by it in 
common with Africa. The proportion of poisonous to innocuous species is likewise 
very high in the Oriental region, and has been estimated at about one in ten. 
Africa has scarcely half the number of snakes found in the Oriental region; and 
it is noteworthy that the forms inhabiting Madagascar have but little in common 
with those of the mainland; the so-called lycodonts, which. are so common in 
Africa, being unknown in Madagascar, while some of the forms from that island 
are closely allied to South American types. Whereas pit-vipers are absent, an 
especial feature of Africa is the number of typical vipers which inhabit that 
country; and Australia, which differs so remarkably from India in its tortoises, 
possesses snakes (and likewise lizards) closely allied to African forms. Next 
to the Oriental region, tropical America is richest in ophidians, although 
the number of generic types is not so great. The proportion of poisonous species 
is, however, high, and has been estimated at as much as one in eight. In Southern 
Argentina and Patagonia snakes become scarce. Unlike its chelonians, the snakes 
of North America present a resemblance to those of Central America. Indeed, 
a feature of the whole of America is the absence of typical vipers, and the 
abundance of pit-vipers, although several genera of the latter are common to Asia. 
Europe and Northern Asia are comparatively poor in snakes, but (next to Africa) 
are characterised by the number of typical vipers and colubrine water-snakes. 
