les of the
peduncle symmetrically arranged in close whorls.

Maxillae, deeply notched: caudal appendages, multi-articulated:
filamentary appendages, none.

Philippine Archipelago, Mus. Cuming: China Sea, Mus. Brit.:
Amboyna and East Indian Archipelago, according to Rumphius and
other authors: Madagascar, according to J. E. Gray.

_Capitulum_, compressed, consisting of the scuta, terga, carina,
rostrum, and a large pair of upper latera, with a single lower whorl of
smaller valves; these latter vary from 22 in very small specimens, to 26
in large specimens. The capitulum, therefore, is formed of at most 34
valves; but in the largest specimen seen by me, the capitulum being 2.3
of an inch in width, there were only 32 valves. In the smallest, namely,
with a capitulum .15 of an inch in width, there were 30 valves. The
valves are remarkably strong, and formed of white shelly matter; they
are closely approximate, and overlap each other: the scuta and terga are
articulated together by a fold; the apices of the valves are either worn
and disintegrated, or they project freely like horns beyond the sack, to
a much greater extent than in any other recent species of the genus:
even a considerable portion of the scuta projects obliquely upwards. The
exterior surfaces of the valves (when not worn) are covered by a strong
yellow membrane, and the upper free parts are generally attached
together for some little length by this same membrane. The valves are
plainly marked by the zones of successive growth; and most of them are
ribbed and furrowed slightly, from their umbones to their basal margins.
The yellow external membrane, examined microscopically, is marked by, or
rather formed of, numerous growth-lines, crossed by longitudinal beaded
ridges. The tubuli are not numerous, and of small diameter.

_Scuta_ (Pl. VII, fig. 3 _a'_, _a_) triangular, with the apex more or
less produced, according to the state of its preservation, and a little
curved towards the terga; basal margin, and in some degree the
tergo-lateral margin, arched, and slightly protuberant; occludent margin
thickened, slightly prominent, with the inner edge covered by the
yellow membrane, like the exterior surface of the valve. The upper part
of the tergo-lateral margin overlaps a little the edge of the tergum,
and receives it in a furrow,--the two valves being thus locked together.
This furrow lies in the freely-projecting, membrane-covered portion, and
ex