106 REPTILES AND BIRDS. 



The family of Helodermidcz is founded on a very remarkable 

 Lizard from Mexico, the H. horriditm, which is of the same size as the 

 Great Dragon, and in some respects approximates to the Old World 

 family of Varanidoe. 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 Varanidce 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 Crocodilidce. 

 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 tnem 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. Gunther 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 



