106 REPTILES AND BIRDS, 
The family of He/odermide is founded on a very remarkable 
Lizard from Mexico, the #. horridum, which is of the same size as the 
Great Dragon, and in some respects approximates to the Old World 
family of Varanide. Its back and sides are covered with oblong, 
hexagonal, very convex and shield-like scales, and the belly with 
oblong, rather convex plates; the tail is cylindrical, with oblong, 
convex scales above, and flat, elongate, thin plates beneath. The 
head is somewhat flattened, and is covered with polygonal, convex 
shields ; the muzzle is rounded ; and the teeth are incurved on the 
inner side of the jaws, with a groove on the front of their inner side. 
The bite of this reptile is said to be severe. 
The family of Varanide inhabit south-eastern Asia and _ its 
islands, Africa, and Australia. In this family are comprised the 
largest of existing Lizards, with the exception of the Cvrocodilide. 
They are very commonly miscalled Iguanas by Europeans and their 
descendants, in the countries where they are found. These reptiles 
have a pyramid-shaped head, more or less elongated, and covered 
with small and scale-like, but not imbricate, shields. Their teeth are 
acute and compressed. ‘The tongue is elongate, slender, terminating 
in a long fork, and is retractile into a sheath at its base. Their scales 
are small, equal on the sides and on the back, and arranged in cross 
rings; those on the belly and tail are square, in cross bands. Tail 
long, and generally more or less compressed. The feet are well 
developed, with five toes on each, which are armed with strong claws. 
Most of them live near water, and they are excellent swimmers, their 
long and compressed tail serving as a propeller. Their movements 
on land are not much less rapid than in the water. Several of the 
species climb trees, and they are more or less nocturnal in their time 
of action... They are exclusively carnivorous, feeding on the different 
water animals, and on the eggs of birds, and likewise on those of 
other reptiles ; some of them are also destructive to ducklings, and 
to various snakes. Dr. Giinther remarks that “their external nasal 
opening leads into a spacious cavity situated in the snout; when the 
animal dives, it closes the nasal aperture, and retaining a certain 
quantity of air in that pouch, or rather in the two pouches, it is 
enabled to remain under water for a prolonged period without the 
necessity of rising to the surface in order to breathe. It is the same 
plan of structure as that with which a large northern seal (Cystophora 
borealis) is provided.” In like manner, the air-bag connected with 
the one developed lung of the Ophidians retains the necessary supply 
of air during the tedious process of deglutition or swallowing. The 
nostrils are variously placed, either midway between the eye and 
