38 
NATURAL HISTORY. [UPPER FLOOR. 
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 Bryx 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 cf Sea-Snakes ( Hydridee , 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 Ackrockordas 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 
Boce, but they are destitute of spurs, and have the nostrils 
and marine habits of the Sea-Snakes; and they are gene¬ 
rally slate-coloured. 
11. The shielded Reptiles, Cataph racta, (Cases land 2,) 
have the body covered with square imbedded shields, and 
have the tympanic bones sunk in the base of the solid 
hard bony skull; the vent is roundish, or linear and 
plaited, and the generative organs are usually simple. 
