FOSSIL REPTILES. 189 



branching towards the teeth in aged individuals, especially in 

 males. Another very marked projection proceeds from the 

 anterior angle of one orbit to that of the other transversely. 

 This is the most remarkable character of this species, and the 

 one from which its name is derived. Behind the eyes, only, 

 are two rather small holes. 



Besides some scales, spread behind the occiput, and which 

 form there in certain individuals a transverse range of tolera- 

 ble regularity, the nape is armed with four transverse bands, 

 very robust, which touch each other, and proceed to join the 

 series of the bands of the back. The first two consist each 

 of four scales, and, consequently, four ridges, the middle ones 

 of which last are sometimes very much effaced. The two 

 others have most frequently but two of these scales with their 

 ridges. 



Of the transverse ranges of the back, two have two ridges, 

 four have six, five have eight, two have six, and four have 

 four. 



But with age, the lateral scales, not much marked at first, 

 assume the form of the others, and two must be added to the 

 number of ridges in each range. In general, it is rare to find 

 two individuals perfectly similar in this respect. 



All these ridges are not much raised, and are nearly equal 

 with one another. Even the lateral ones of the base of the 

 tail predominate but httle over the others. It is only at their 

 juncture that they become very projecting. 



There are eleven, twelve, or thirteen ranges before this 

 union, and twenty-one after. But these numbers vary. 



This species grows to a considerable size ; some being 

 eleven, and some fourteen feet in length. 



The Yacare of M. D'Azara (which is the present species) 

 proceeds no further south than the 32d degree — precisely the 

 same limit which bounds the northern extension of the pre- 

 ceding species. In the flat island of Marajo, or Johannes, at 

 the mouth of the Amazon, these animals remain in summer 



