CROCODILTA. 39 



The occipital region of the skull (T. VI, fig. 2), in the proportion of its breadth to 

 the depth of the lateral parts formed by the conjoined paroccipitals (4) and mastoids (8), 

 resembles that of the true Crocodiles rather than that of the Alligators, in which that 

 region is proportionally deeper than in the Crocodiles ; the vertical extent of the 

 supraoccipital is less, and that of the conjoined parts of the exoccipitals above the foramen 

 magnum is greater ; the vertical extent of the descending part of the basioccipital is 

 also greater in proportion to its breadth than in the Alligators. The proportion of the 

 ■basisphenoid (5) and of the conjoined parts of the pterygoids (24) which appear in this 

 view (fig. 2), is less than in the Alligators, but is greater than in most Crocodiles, thus 

 presenting an intermediate character ; but the entire exclusion of any part of the 

 posterior nostril from this view is a character of the Alligators, and is due to the 

 horizontal plane of that aperture in them, and to its position in advance of the posterior 

 border of the pterygoids, from which it is partitioned off usually by a bony ridge. 

 The posterior nostril has the same position and aspect in the Crocodilus Hastingsice, 

 and these characters of the posterior nostril are perhaps more distinctive between 

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

 both from the Alligators and from 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 T .VI, 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 champsdides. 



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, torn. cit. The Croc. Hastingsits, 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 niger, 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 Hastingsite the proportions of 

 the lateral temporal apertures (T. VI, fig. 1, 12, 26) and orbital (11, 14, 73) apertures, 

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



