50 
POPULAK SCIENCE EEVIEW. 
relative, the true sea-serpents are of small size. They are 
viviparous. They feed on fishes, never voluntarily quit the 
water, and soon die when brought on shore. 
The peculiarily situated nostrils and high flattened tail — 
characters obviously connected with their mode of life, not to 
speak of the exceptional arrangement of their head-shields — at 
once separate the Hydrophidse from the preceding families, and 
indeed from all other snakes. 
There, is however, one genus of Hydrophids, Platurus, which 
makes a near approach towards the Elapidse. The number and 
disposition of its head-shields is almost identical ; its nostrils- 
are lateral, not superior. “ The poison-fang is short, and not 
followed by a series of other simple teeth, as in Hydrophis. A 
very small single tooth is implanted at some distance behind 
the poison-fang, and is frequently lost. These snakes have 
quite the physiognomy of an Elaps, and the cleft of the mouth 
is not turned upwards behind, as in other sea-snakes.” * 
The families of venomous snakes show well marked peculi- 
arities of geographical distribution. Thus we may consider 
America as the head-quarters of the Crotalidse, Africa of the 
Viperidse, Australia of the Elapidse, and the Indian Ocean of 
the Hydrophidae. 
The Crotalidse are absent from Europe, Africa, and 
Australia. Asia contains several species of this family, but 
they are smaller in size, and far less venomous than those of 
America. When we consider their highly modified structure 
as well as their geographical range, it might reasonably be con- 
jectured, from the point of view afforded by Mr. Darwin’s 
hypothesis, that the Crotalidse first appeared at a later period 
than any other family of snakes, and that in all probability 
their American have succeeded their Asiatic representatives.f 
The Viperidse, on the other hand, are quite wanting in 
America. But two species are found in Asia, one of which is- 
likewise African. Three European species are well known. 
One of these, the common adder (Vipera berus), extends its 
range to England and Scotland, but not to Ireland. Another 
species, the ^so-called Death-adder (Vipera acanthophis) is the 
sole representative of its family in Australia.i 
* Quoted from Dr. Giinther’s “ Reptiles of British India,” which contains- 
a critical revision of all the Hydrophidae known in 1864. Before this date 
the species of sea-snakes were in a state of thorough confusion, in conse- 
quence of the half-attempts made by previous naturalists to explain their 
character. 
t So that snakes have been preceded by the other orders of Reptiles, 
venomous by non-venomous snakes, viperine by venomous coliibrine snakes,, 
and Crotalidae by Viperidae. 
I Australia is further remarkable for the disproportion between its^ 
