early stages of growth, (as explained under _S. vulgare_,) and,
therefore, they form a depressed rim.

_Rostral Latera_, almost exactly triangular, curved; basal margin
furnished with a just perceptible rim.

_Infra-median Latera_, quadrilateral, sides unequal in length; the
carino-basal margin being the longest; in area not quite twice double
the rostral latera; directed obliquely upwards.

_Carinal Latera_, sub-triangular, produced upwards, with the apex
rounded, and the two lateral margins hollowed out; the basal margin
exceeds a little in length the basal margin of the rostral latera. The
umbones of these two latera are seated at their basal outer angles, so
that the growth of the valves is towards each other and upwards. The
umbo of the infra-median latus is seated at the baso-rostral angle, and
hence the growth is obliquely upwards. The umbones of the rostral latera
must have been close together, over the unknown rostrum.

_Length_ of capitulum about 4/10th of an inch.

_Peduncle_, only small fragments are preserved; the calcified scales are
small, closely imbricated, several of them together only equalling in
length the basal margin of the rostral latera. Each scale is thin,
transversely elongated; basal imbedded portion straight; upper margin
rounded.

_Mouth._--Labrum with the upper part highly bullate, forming an
overhanging projection; palpi apparently small and narrow.

_Mandibles_, narrow, produced, with three teeth; inferior angle
pectinated, as is sometimes the third tooth; the distance between the
tips of the first and second teeth equals that between the second tooth
and the inferior angle.

_Maxillae_, extremely narrow, produced, without any notch; spinose edge
exactly one third of the length of the mandibles: beneath the two upper
great spines there are only three or four pair of spines; on the convex
upper margin there are some minute tufts of the smallest hairs.

_Outer Maxillae_, rounded with the inner margins very sparingly but
continuously covered with bristles. I could not ascertain whether the
olfactory orifices were tubular.

_Cirri._--These consisted, in the one specimen, of merely small
fragments. The segments of the posterior cirri are elongated, not
protuberant, and support, I believe, five pair of non-serrated spines,
and an exterior row of very minute spines: dorsal spines fine and long.
Either the second or third cirri, or probably both, are remarkable for
having the whole