d at intervals: the apex smooth and
pointed; the exterior surface longitudinally and finely ribbed, like the
valves. The spines increase irregularly in size from the bottom to the
top of the peduncle, those at the carinal and rostral ends being
generally the longest; they point upwards and hide the bases of the
valves. They are not arranged symmetrically, and new ones are formed
over all parts of the peduncle. They are formed of the same substance as
the valves, and do not contain any calcareous matter. These horns are
yellowish, generally ringed with pale and dark blueish brown, which on
pressure becomes slightly opalescent with pale blue and fiery red:
sometimes only the upper horns are thus ringed, and in rare instances
all are simply yellowish. The muscles of the peduncle run up to the
bases of the four valves.

_Surface of Attachment._--The cement appears to proceed from only two
points. In some specimens, a considerable length of one side of the
peduncle was fastened to the surface of attachment, the horns or spines
being enveloped in the cement. The prehensile antennae of the larva will
presently be described under the male.

The _length_ of an average specimen, including the peduncle and valves,
is about half an inch, and the width across the widest part one fifth of
an inch. Mr. Cuming has one specimen an inch in length, but this is
owing to the peduncle being unusually tapering. In a specimen kept some
years in spirits, the cirri, trophi, caudal appendages, and corium under
the membrane between the scuta, were all dark purple; the sack and
corium of peduncle clouded with purple, and the prosoma pale-coloured.

The _Body_ (Pl. IV, fig. 8 _a'_) is small compared with the capitulum
and peduncle; it is much flattened; the prosoma is of a very peculiar
shape, being square, the sides of equal length, and, in an average-sized
specimen, 75/1000th of an inch long. The peculiar shape arises from the
great distance between the first and second cirrus--from the mouth being
far removed from the adductor scutorum muscle--and lastly, from the
lower part of the prosoma being not at all protuberant. The thorax which
supports the cirri is also unusually small, plainly articulated, and
separated from the prosoma by a deep fold. The thin membrane of the
prosoma is studded with some fine, pointed hairs, about 3/400ths in
length, and articulated on little circular discs.

_Mouth_, placed at a considerable distance from the adduc