84 AUSTRALIAN SNAKES. 
be of no tse to snakes moving through a fluid, and not over a rough hard 
surface, and therefore they are either only rudimentary or entirely absent. 
The genus Platurus, however, is a most remarkable exception, in having 
ordinary ventral shields; and this circumstance, together with the lateral 
position of its nostrils, induce me to believe that these serpents frequently 
go on shore, sporting or hunting over marshy ground. In many Sea 
Snakes the hind part of the body is curved and. prehensile, so that they 
are enabled to secure a hold by twisting this part of the body round corals, 
seaweeds, or any other projecting object. Their tail answers all the pur- 
poses of the same organ in a fish, and their motions in the water are almost 
as rapid as they are uncertain and awkward when removed out of their 
proper element. Their nostrils are placed quite at the top of the snout, 
as in Crocodiles and in Fresh Water Snakes, so that they are enabled to 
breathe whilst the entire body and the greater part of the head are im- 
mersed in water. These openings are small and subcrescentic, and provided 
with a valve interiorly, which is opened during respiration, and closed when 
the animal dives. They have very capacious lungs, extending backwards 
to the anus, and consequently all their ribs are employed in performing 
the respiratory function ; by retaining a portion of the air in these exten- 
sive lungs, they are enabled to float on the surface of the water without 
the slightest effort. 
“The ‘ scales’ of the Sea Snakes are frequently very different from 
those of other snakes; they overlap one another in only a few species 
(Platurus, Hydrophis stokesii, and belcheri); in others they are but little 
imbricate and rounded behind, and, again, in others they are of a sub- 
quadrangular or hexagonal form, placed side by side, like little shields ; 
the less imbricate they are, the more they have lost the polished surface 
which we find in other snakes, and are soft, tubercular, sometimes porous. 
The form and the arrangement of the scales afford good specific characters, 
but it is necessary to observe that they generally differ in size, arrange- 
ment, and form, in the different parts of the body. In my descriptions I 
have always counted the series of scales on the neck—that is, at a distance 
from the head about equal to its length, having found that the numbers at 
that place are least subject to variation in different individuals; whilst I 
have taken the characters of the form or arrangement of the scales from 
those in or behind the middle of the body, the scales on the neck being 
narrow and more or less imbricated in almost all the species. 
