PURBECK CROCODILES. 649 



The Immerus (fig. 10), preserved near the jaw, shows the usual Crocodilian characters, 

 with more slender proportions than in Crocodilus niger ; it rather resembles that of the 

 Gavial.i 



The characters of Nannosuchus yielded by the foregoing specimens are supplemented 

 by those of the skull represented of the natural size in PL 44, fig. 1. The teeth 

 preserved in situ and detached, but in contiguity with the alveolar border, are generically 

 those to which they would be opposed assuming the skull to be that of a Nannosuchus. 

 The inferiority of size is not shown by any other distinctive character to indicate a 

 species other than that founded on the lower jaws above described. 



As in those, the teeth of the upper jaw are divided by intervals usually greater than 

 their basal breadth. Each premaxillary (fig. 1, 22) had four teeth at least; the maxillary 

 had not fewer than ten teeth. 



The characters of length and slenderness of crown in the teeth of this small Crocodile 

 suggested a comparison of its skull with that of Petrosuchus, but the differential 

 characters exceed in importance those of size. The upper jaw of Nannosuchus does 

 not contract so rapidly, or in so great a degree in advance of the orbits, as in Petro- 

 suchus (PI. 41) ; it is also shorter as well as broader; no amount of growth could have 

 converted it into the slender elongate shape which approximates Petrosuchus to the 

 gavial-like Crocodilus catcqjhr actus. 



The hind border of the parieto-mastoid platform is undulate ; gently convex at the 

 middle, where it is formed by the parietal (ib., 7), concave on each side, where it is carried 

 out by the mastoids (ib., 8). 



In Crocodilus niger this border is straight; in Croc. palusfris it is undulate, but the 

 middle parietal convexity is much less than the lateral, concave, mastoidean curves, 

 owing to the relatively narrower extent of the parietal bone. The lateral borders of the 

 supra-cranial platform, due to the mastoids (ib., 8) and post-frontals (ib., li), present, in 

 Nannosuchus, a gentle sigmoid curve. In most modern Crocodilia these borders are 

 straight, running parallel in Croc, niger, slightly convergent forwards in Croc, cafa- 

 phr actus and Croc, intermedius. 



The breadth of the platform is to that of the skull, taken across and including the 

 zygomatic arches, as 8 to 10 in Nannosuchus ; in Croc, niger the platform is little more 

 than half the breadth of the skull taken across the hind part of the parieto-mastoid or 

 upper temporal apertures ; in Croc, jjalustris the platform occupies half the breadth 

 of the skull taken at the same part. 



The upper temporal apertures (t) have the same relative size as in Petrosuchus, but 

 they differ in shape, being less circular, the longer diameter being longitudinal, or in 

 the skull's axis. As far as the orbits are preserved these do not exceed in size the 

 upper temporal apertures. This character of the Mesozoic Crocodile is retained in the 

 present dwarf species. A super-orbital bone strengthened the upper eyelid ; it retains 



1 'Catalogue of Osteology, Mus. Coll. Chir.,' 4to, 1853, p. 153, No. 691. 



