82 MAEINE REPTILES OF THE OXFORD CLAY. 



defined, may be synonyms of Steneosawus, but need not be referred to here. A com- 

 plete history of the genus is given by Deslongchamps in his ' Notes Paleontologiques,' 

 p. 95 (1867), and also more recently by L>r. Erwin Auer in his important paper 

 "Ueber einige Krokodile der Juraformation " (Palaeontographica, vol. lv. (1909) p. 219 

 et seqq.). 



Skull (Pis. V.- VII. ; text-figs. 31-33). — The following account of the skull in this 

 genus is founded, so far as possible, on a nearly complete and comparatively uncrushed 

 skull of Steneosaurus leedsi (R. 3806) found in association with a nearly perfect 

 skeleton. 



It may be noted that in the case of the skulls of the various species of Crocodiles 

 from the Oxford Clay of Peterborough, the bones do not, as a rule, become separated 

 from one another, as is often the case with skulls of the Sauropterygia, and con- 

 sequently it is not possible in any case to describe the individual bones in such detail 

 as has been done, for instance, with the occipital and auditory bones of Peloneustes 

 (see above, pp. 35-39, text-figs. 11-12). Indeed, the dorso-ventral crushing undergone 

 by most of the skulls of Steneosaurus makes it very difficult to determine the form 

 and arrangement of their constituent elements, particularly in the cranial portion, and 

 the difficulty is still further increased by the obscurity of the sutures. 



The premaxi 'lice {pmx.) are small bones forming the expanded anterior end of the snout 

 and completely surrounding the external narial opening (nar.). This extends nearly 

 the whole width of the expanded portion of the snout ; its anterior border is thickened 

 and rounded, and in the middle line where the two premaxillae meet, it is raised into a 

 small prominence. The posterior border, which is also rounded and thickened, is nearly 

 straight in most specimens, but this seems to be in part the consequence of the com- 

 pression to which the bones have been subjected ; in the middle of the posterior border 

 there is a slight projection. The middle of the floor of the narial opening is occupied 

 by a small incisive foramen, which is about twice as long as wide. Behind the nostrils 

 the broad facial processes of the premaxillae extend back between the maxillae to a point 

 about opposite the third maxillary tooth. On the palatal face, on the other hand, the 

 maxillae usually send forwards a tongue-like process between the premaxillae as far as the 

 level of the anterior edge of the alveolus of the fourth premaxillary tooth. The palatal 

 surface of the united premaxillae is gently concave from side to side and bears, near its 

 middle, the incisive foramen to which reference has been made. Each premaxilla 

 bears four teeth : the anterior pair are close to the middle line, the walls of their 

 alveoli being separated by a small notch between the anterior end of the bones ; they 

 are the smallest. Behind and a little to the outer side of these is the next pair, which 

 are somewhat larger. Behind these there is a diastema, the surface of which is 

 concave from before backwards and convex from side to side. Then come the sockets 

 for the third and fourth teeth, which are immediately behind one another and separated 

 only by a narrow alveolar wall : these two teeth are large and nearly equal in size. 



