Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/498

 Fig. 3. — Scales of Gyrodus coccoderma.

Mr. Etheridge having kindly directed my attention to some specimens of Pycnodont teeth deposited in Jermyn Street hy Mr. Mansel, I found amongst them a fine example of the vomer of a Gryrodus (fig. 4), which, from its size, may very possibly have belonged to Gyrodus coccoderma. This conjecture is strengthened by the fact that it was found in the same stratum and in the same locality, viz. in the Kimmeridge Clay of Kimmeridge. The dentigerous area of the bone measures two inches and eight-tenths in length. The breadth at the base is one inch and three-tenths, and at the apex seven-tenths of an inch. It is furnished with five rows of teeth. The median row contains nine large circular tritores, much abraded on the grinding surface. A tenth tooth is wanting at the base. Next in size come the marginal rows. One of these contains fourteen, the other (imperfect) thirteen teeth. They differ in form from those of the median row in having the outer periphery truncated, and the outer edges raised. Although somewhat used, they still retain the gyrations characteristic of the genus. The intermediate row contains the smallest teeth. There are fourteen in each row, rather irregular in form, but more or less circular. The surfaces are deeply furrowed, as they have suffered little from use. This specimen differs from all the vomerine remains of Gyrodus yet figured ; it approaches more nearly to a species named Pycnodus Dutertrei by M. E. Sauvage, from the Portlandian rocks of Portel, which may possibly be a Gyrodus having the teeth much worn;