220 PKOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



covered base ; this base is widely excavated by a conical pulp-cavity, 

 which ends rather suddenly. The outer surfaces of the teeth are 

 flatter than the inner ones, which are almost semicircular ; this is 

 strongly marked in the case of fig. 3, in which the backward curve 

 completely overbalances the incurvation. 



It is evident that figs. 1 and 2 could only have belonged either to 

 the right side of the lower or to the left side of the upper jaw, and that 

 fig. 3 occupied a position either on the left side of the lower or the 

 right side of the upper jaw among the posterior teeth, which pro- 

 bably, as in Pliosaiirus, were both smaller and more recurved. 

 Fig. 4, a more compressed form, is perfectly symmetrical and must 

 be allowed to have had a place among the most anterior teeth, if one 

 be guided by the fact that these, in existing Crocodiles {e. g. in C. 

 hiporcatus), gradually become symmetrical as they approach the 

 middle line. To the fragmentary tooth, reduced perhaps to its pre- 

 sent condition in the anima?s mouth, may be assigned the same sides 

 of the jaw as fig. 3. 



Scattered over the four entire teeth are several faint constrictions 

 or annular depressions, very similar to the effect produced upon the 

 finger by a tightly fitting ring (fig. 2). 



The enamel is very thin, and shows under a lens of moderate power 

 inconspicuous longitudinal wrinkles. 



The greatest length of the largest tooth (fig. 1) is 2 inches 8 lines ; 

 its transverse diameter at the base =11 lines; its antero -posterior 

 diameter, also at the base, =1 inch 1 line. 



Similar measurements, taken about | in. from the apex of the 

 same specimen, give 6 and 9 lines respectively. 



Teeth similar in their essential characters to those described and 

 figured above, and differing from them only in such trifling matters 

 as the presence of enamel ridges and constrictions below the crown, 

 are to be seen in the anterior region of the mouth in all recent (true) 

 Crocodiles and Alligators ; but in these the posterior teeth, both in 

 the upper and lower jaw, differ enormously from the anterior ones — 

 a fact of considerable importance, and one that may well serve as a 

 caution to the palaeontologist who is disposed to found a genus or 

 species upon characters furnished by a single tooth. 



To conclude, the crenulation of the trenchant ridges is by no 

 means peculiar to the teeth under consideration, but is observable, to 

 a greater or less extent in those of all Crocodilian reptiles * that I 

 have ever examined, from the remotest known ancestor to the living- 

 representatives of the order — in a word, from the Triassic Belodon f 

 (an indubitable crocodilian) to Crocodilus bombifrons, which, with its 

 congener C. biporcatus and the Gavial, preserves its destructive ex- 

 istence in the waters of the Ganges. 



^ Unworn teeth of the Crocodihan genera Jacare, Mecistops, and Bhi/nchosuchus 

 have not yet fallen under my notice, but I have succieeded in tracing crenulation 

 plainly in teeth of Steneosaurus, and more faintly in those of Teleosaurus and the 

 Gangetic Gavial. 



t It is only right to state that I was led to examine the remains of this rep- 

 tile contained in the British Museum, as well as Von Meyer's figures (" Muschel- 

 kalksaurier,'' tab. 20. fig. 6, Palseontographica, Band. x. Taf. 38-40 &c.) by Prof. 

 Huxley's statement of its Crocodilian affinities. 



