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;
