CROCODILTA. 123 



Alligator and Crocodile than the shape of the aperture, in which the present fossil 

 differs from botli the Alhgators and most of the Crocodiles with which I have compared 

 it. The backward extension of the exoccipitals and of the basioccipital condyle, is 

 such as to bring both parts into view in looking directly upon the middle of the upper 

 surface of the skull, as in PI. 1 J, fig. 1 . In this character the fossil resembles the 

 Crocodiles more than the Alligators, but the projection is greater than in existing 

 Crocodiles, and equals that in the Sheppy Crocodilus cliamjisoidcs. 



On the upper surface of the skull a distinctive character has been pointed out by 

 Cuvier in the different proportions of the supra-temporal apertures in the Alligators 

 and Crocodiles. The horizontal platform in which these apertures are perforated, is 

 also square in the Alligators ; the mastoidal angles being less produced outwards and 

 backwards, and the postfrontal angles less rounded off ; this difference is shown in the 

 skulls figured in Cuvier's pi. i, tom. cit. The Croc. Hastuiffsice, both by the obtuseness 

 of the postfrontal angles, and the acuteness and production of the mastoidal angles, 

 resembles the Crocodiles, as well as by the size of the supra-temporal apertures ; these 

 are ovate with the small end turned forwards and a little outwards. 



Another character may be noticed in the figures of the skulls of the three species 

 of Alligators as compared with those of the three species of Crocodile in Cuvier's 

 pi. i, viz. the larger proportional size of the orbits in the former, in which the orbit 

 much exceeds in size the lateral temporal aperture. In the Alligator niffer, also, I find 

 the orbits enormous, and it is the encroachment of the narrow anterior part of the orbital 

 cavity upon the facial part of the prefrontal and lachrymal, that renders that part of those 

 bones relatively shorter in the Alligators. In the Crocodilus Haslingsm the proportions of 

 the lateral temporal apertures (PI. 1 A, fig. 1, 12, 2C) and orbital (11, u, 73) apertures, 

 are like those in the species of Crocodile in which the orbits are smallest. The extent of 

 the facial part of the prefrontal (14) and lachrymal (73) is greater in the Croc. Ilastinr/sia 

 than in any existing species of true Crocodile. Another characteristic of the present 

 fossil presented by the upper surface of the skull, is the shortness as well as breadth of the 

 nasal bones, and their almost truncate anterior termination at nearly one inch from the 

 external nostril. In all the Alligators' skulls that I have examined or seen figured, 

 the nasal bones are broadest at their posterior third part, and converge to a point 

 anteriorly, where in the Alligator lucius, e. g., they extend across the nasal aperture. 



The interorbital space is slightly concave in the Crocodilus Hastingsice ; two broad 

 and slightly elevated longitudinal tracts are continued forwards upon the face from the 

 fore part of the orbits ; but they are not developed into ridges, as in the Croc, biporcatus. 

 The maxillaries swell out a little in advance of the middle of the nasals, and then 

 contract to the crocodihan constriction at the suture with the premaxillaries, where the 

 tips of the lower canines appear in the upper view (fig. 1, PL 1 A), and their whole 

 crown is exposed in the side view (fig. 1, PI. 1^. The conjoined parts of the 

 premaxillaries send a short pointed projection into the back part of the exteraal nostril. 



