286 ME. E. LTDEKKEE ON A CEOCODILIAN JAW 



Compared witli the Crocodilians from the Oxford and Ximeridge 

 Clays described by Deslongchamps, in his ' Notes Paleontologiques,' 

 under the names of Steneosaurus and Metriorhynchus, the present 

 specimen differs, among other features, from all those species of 

 which the mandible is known, by the smaller number of teeth, this 

 character alone being quite sufficient to prove its generic distinct- 

 ness from Steneosaurus. In the mandible of a typical species of 

 MetriorhyncJius, like M. Moreli (Deslongchamps, op. cit. pi. xxii., 

 and fig. 1 of the diagram illustrating this paper), there are nineteen 

 alveoli, of which the first four are larger than the others, and are 

 separated from one another by considerable intervals, so that the 

 anterior portion of the mandible is quite unlike the specimen before 

 us. In 31. hracliyrliynclius of the Oxford Clay {op. cit. pi, xxiii.) 

 the number of alveoli in the upper jaw was less than in M. Moreli ; 

 but if Deslongchamps is correct in his restoration of the muzzle, the 

 extremity of the mandible must have been similar to that of M. 

 Moreli^ and in any case the number of lower teeth (judging from 

 the relative number of upper and lower alveoli in the latter) can 

 scarcely have been less than fifteen. It may therefore be safely 

 considered that the specimen cannot be referred to the genus 

 MetriorhyncJius, and also that it is specifically distinct from all the 

 forms which have been described under that name. 



The genus Teleidosaurus * of the Fuller's Earth (which in some 

 respects connects Steneosaurus with MetriorhyncJius) makes a deci- 

 dedly nearer approach to the present specimen, as is shown by the 

 reduction in the number of the teeth and the great width of the 

 oral aspect of the skull. In T. Oalvadosi and T. Joherti the num- 

 ber of lower teeth is, however, 20 or 21 ; and the anterior alveoli 

 are spaced, with a very long interval between the 4th and 5th in 

 T. Joherti. 



If, however, our specimen be compared with the large Crocodilian 

 originally described from the Kimeridgian of France under the name 

 of MacJiimosaurus moscef, and to which I have referred J the mandible 

 and part of the cranium from the equivalent beds of Dorsetshire 

 figured by Sir E. Owen § as Pliosaurus trochanterius, we shall find 

 a marked resemblance between the two. In both specimens the 

 number of alveoli is very nearly the same, the Kimeridgian one 

 having 14 on each side ||, and the present one 13 on one side and 

 12 on the other. In both the splenial extends as far forward 

 as the seventh alveolus ; while the anterior alveoli in both are 

 not separated from one another by longer intervals. The Oxfordian 

 mandible is, indeed, rather more pointed at the extremity of the sym- 

 physis, and is perhaps more flattened at the symphysis. The total 



* See Deslongchamps, oj). cit. pis. xviii., xix. 



t See Sauvage & Lienard, Mem. Soc. Geol. France, ser. 3, toI. i. j^I. xxiii. 



X Cat. Foss. Kept. Brit. Mus. pt. i. p. 104. 



I Reptiles of the Kimeridge Clay (Mon. Pal. Soc. for 1868), pt. 3, pi. iii. 

 figs. 3-5. 



II In the British Museum Catalogue it is stated that there are 13 alveoli, but 

 the anterior one is evidently broken away on either side. 



