IGUANOID GROUP. 129 



western half of the globe, two genera occurring in Madagascar, and a third in 

 the Fiji and Friendly Islands. Although, with these exceptions, the family is 

 unknown in the Old World, the same perverseness which causes Anglo-Indians to 

 speak of the Oriental crocodiles as alligators, leads to the monitors of the Old 

 World being commonly termed iguanas, although few lizards are more unlike 

 than the members of these two groups, both as regards external and internal 

 characters. In their general structural features the iguanoids come very close to the 

 agamoids. Thus in both groups the head is covered with numerous small shields ; 

 while the back is clothed with scales of different kinds, which are often arranged 

 in oblique rows. Similarly, the eyes have round pupils and are furnished with 

 well-developed lids, and the drum of the ear is frequently exposed. Both groups, 

 again, have two pairs of limbs, which may be relatively longer or shorter in the 

 different genera, but are each provided with five toes. The length of the tail is 

 subject to a large amount of variation, although it generally exceeds that of the 

 head and body. Moreover, the two families resemble one another in the form and 

 structure of the tongue, which is thick, short, scarcely notched, and generally fixed 

 to the floor of the mouth throughout its length. When, however, we come to 

 contrast the teeth of iguanoids with those of agamoids, we find a striking difference 

 which at once serves to draw a sharp line of distinction between the two families. 

 As we have already seen, in the latter group the teeth are attached to the very 

 summits of the bones of the jaws (acrodont), and are commonly differentiated into 

 front teeth, tusks, and cheek-teeth. In the iguanoids, on the other hand, the tall 

 and cylindrical teeth are attached by their sides to the outer wall of the jaws in 

 the so-called pleurodont manner; the whole series being generally more or less 

 uniform in character, and without any large projecting tusks. In the typical 

 iguanas the teeth have somewhat diamond-shaped compressed crowns with serrated 

 edges ; and it was from a superficial resemblance to this type of tooth that the 

 teeth of the great dinosaurian reptile from the English Wealden received the name 

 of Iguanodon. A few genera, again, have the teeth divided into three lobes, thus 

 resembling a fleur-de-lis. Many species of the family are further characterised by 

 having teeth on the pterygoid bones of the palate, while a single genus is one of 

 the few lizards in which there are teeth on the palatine bones. 



The iguanoids, which comprise about three hundred species, arranged in fifty 

 genera, may be regarded as especially characteristic of South and Central America, 

 although they extend into the warmer parts of the northern half of that continent, 

 ranging in the west as far as British Columbia, and in the east to Arkansas 

 and the Southern United States, while they are also represented in many of the 

 American islands. Their occurrence in Madagascar (where, as in America, 

 agamoids are wanting) has been already mentioned, and it is probable that this 

 remarkable instance of discontinuous distribution may be explained by the 

 occurrence of fossil remains of species of the family in the upper Eocene rocks 

 of France, where agamoids seem likewise to have been wanting. 



Very variable in external appearance, iguanoids present equal diversity in 

 their modes of life, and it is not a little curious that, with the exception of the 

 flying lizard, almost every group of the agamoids finds a parallel, both as regards 

 structure and habits, in the present family ; the two families being thus repre- 



vol. v. — 9 



