OCTOMERIS. _G. B. Sowerby._ Zoological Journal, vol. 2, p. 244, July,
1825.
_Compartments eight: radii with their edges crenated: basis membranous._
_Distribution_, Cape of Good Hope; Philippine Archipelago.
The two species of this genus differ considerably in external
appearance, though not in essential character. Both, as the name
expresses, have eight compartments: the carino-lateral pair are
rather narrower than the lateral. The basis is membranous. The radii
are narrow, and are distinctly crenated on both sides of the sutures
with the teeth neatly interlocking; but these teeth can hardly be
distinguished in the large, corroded specimens of _O. angulosa_. The
crenated structure of the radii is identical with that described
under _Chthamalus dentatus_ and _Hembeli_; if, indeed, we were to add
carino-lateral compartments to the shells of these two species, they
would belong to Octomeris. I have seen only a few specimens of either
species of Octomeris, and none preserved in spirits; and therefore I
know nothing of the anatomy of the softer parts: I was not able to make
out distinctly any branchiæ. The cirri differ considerably in the two
species, in nearly the same way as in the two species of Chamæsipho. In
the structure of the second pair of cirri, and in the tendency of the
basal margin of the parietes to form bay-like indentations, _Octomeris
angulosa_ shows some special affinity to _Chamæsipho scutelliformis_.
Under Pachylasma, I stated that that genus was closely related to
Octomeris; and I have just alluded to the close affinity of the latter
to the division of the genus Chthamalus, which has crenated radii.