seen internally, irregularly rhomboidal, ending downwards in
a blunt point, of which the two sides, (neither being sensibly hollowed
out,) stand at about an angle of 45 deg. to each other. Scutal margin,
with the upper part, (as above remarked,) slightly protuberant: near the
bottom of this margin, there is a very slight projection, answering to
the small knob at the baso-tergal angle of the scutum. Externally,
towards the basal angle, the narrow strip not concealed by the
overlapping of the latera and carina is square-edged, with the zones of
growth on it straight.

_Carina_, internally concave in the upper free part, with a slight,
central, internal crest, caused by the projection of each successive
zone of growth. The inner growing surface is almost pentagonal in
outline; with the basal margin square and truncated in the middle.

_Rostrum_ (fig. 2 _a_), rather conspicuous, many zones of growth being
preserved. It equals in width six of the subjacent scales of the
peduncle, but as these are rather smaller than elsewhere, the width
equals about five of the ordinary uppermost scales; compared with the
latera, it is nearly 5/7ths of their width.

_Latera_, unusually large; as seen on their interior surfaces, (or in a
section parallel to the zones of growth,) they are triangular, elongated
transversely, with the carinal angle a rectangle. In width they equal
the seven subjacent scales of the peduncle, and are more than half as
long as the basal margin of the carina.

_Peduncle_, with the upper scales varying from circular to
quadrilateral, thrice as large as those in the second whorl; beneath
which, in the next three or four whorls, the scales rapidly decrease in
size; and beneath these the whole peduncle is studded with equal-sized,
rounded, calcareous beads, so minute as to be quite invisible to the
naked eye. This specimen was nearly ready to moult, and perhaps in
consequence of this, even the upper scales were most obscurely serrated
on their lower margins, and all the others quite smooth: there were some
much worn horny spines close to the bottom of the peduncle. Basal
calcareous cup slightly concave, of moderate size; its diameter, in the
one specimen examined, was 9/10ths of an inch; it was composed of
several layers. In the specimen figured (2 _a'_) by Reinhardt, instead
of a cup, there is a straight row of small discs, which are attached to
the walls of the cavity, as explained in the generic description.

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