34 NATURAL HISTORY. [UPPER FLOOR. 
In the two last groups the fangs are most commonly 
found intermingled with the teeth. 
The family of Boas ( Boidce, Case 13) have usually a short 
body, with narrow plates on the abdomen, and a short co¬ 
nical tail, furnished with two short crooked spurs at its 
base. These spurs have lately been shewn to be analogous 
to the hinder legs of other reptiles. The eyes and nostrils 
are lateral, the former have an elongated oval pupil, and 
the tail is conical and prehensile. The Boas are not 
venomous; they kill their prey by crushing it between 
the folds of the body, generally, at the same time, twisting 
the end of the tail round a tree, or some other fixed point, 
in order to increase their power. The American kinds 
(Boa ) have only a single row of plates beneath the tail; 
they vary greatly in respect to the structure of the scales 
on the head and lips. Some of the Indian species, as the 
Netted Boa, ( Boa regia,) have a single series of plates, 
whilst most of the other species have two rows (Python). 
The Eryx differs from the other Boas in having a cylin¬ 
drical body, a very short tail, and the head covered with 
scales similar to those of the back. Cuvier says that this 
genus has no spurs, but the specimen in the British 
Museum shews them distinctly. 
The family of Sea-Snakes ( Hydridce , Case 13) are easily 
known by their compressed form, narrow scale-like ventral 
shields, and vertically flattened tail. Their hinder limbs are 
not developed. The eyes and nostrils are vertical and the 
pupil round. These reptiles, which are peculiar to the 
seas of Asia and New Holland, are in some degree poi¬ 
sonous, many of the species having small fangs, dispersed 
amongst the true teeth. Some have a small head, and the 
body covered with scales, ( Hydrus ); the others have a large 
head and broad neck, and the body covered with embedded 
square plates, placed in longitudinal series, as Pelamis . 
The AchrGchordus has the habits and many of the cha¬ 
racters of the Sea-Snakes; but its body and head are 
covered with rough granular scales, and its tail is conical. 
It is found in the rice-fields of India. The Chersydrus 
has the scales of the Achrochordus but the tail is com¬ 
pressed, as in the other Sea-Snakes. The Homalopses 
have the narrow belly plates, the form and scales of the 
Bote, but they are destitute of spurs, and have the nostrils 
