Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/314

220 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 probably, as in Pliosaurus, 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. biporcatus), gradually become symmetrical as they approach the middle line. To the fragmentary tooth, reduced perhaps to its present condition in the animal'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 3/4 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 (an indubitable crocodilian) to Crocodilus bombifrons, which, with its congener C. biporcatus and the Gavial, preserves its destructive existencein the waters of the Ganges.