vol.
x, 1825.

PENTALEPAS VITREA. _Lesson._ Voyage de la Coquille. Mollusca, Pl.
xvi, fig. 7, 1830.

ANATIFA OCEANICA (!) _Quoy_ et _Gaimard_. Voyage de l'Astrolabe,
Pl. xciii.

_L. valvis glabris, tenuibus, pellucidis; carina rectangule flexa, parte
inferiore in discum planum oblongum expansa._

Valves smooth, thin, transparent; carina rectangularly bent, with the
lower part expanded into a flat oblong disc.

Filaments, five on each side; segments of the three posterior cirri with
triangular brushes of spines.

Var. (_Donovani_, of Leach.) Carina with the upper part flat,
spear-shaped, externally with a narrow central ridge.

Var. (_Villosa._ Pl. I, figs. 6 _b_, _c_.) Valves placed rather distant
from each other; carina extremely narrow, with the upper part of nearly
the same width throughout; terga with the lower part much acuminated;
body of animal finely villose.

Coasts of Great Britain and France; Baltic Sea, according to
Montagu Southern United States (from Agassiz); tropical Atlantic
Ocean; East-Indian Archipelago, off Borneo and Celebes; Pacific
Ocean, between the Sandwich and Mariana Archipelagos; New
Zealand: attached to fuci, Spirulae Janthinae, Velellas, often to
feathers and cork; often associated with the young of _L.
anserifera_, (var. _dilatata_,) and _L. pectinata_.

_General Appearance._--Capitulum highly variable in all its characters;
thick and broad in proportion to its length, but the breadth is
variable,--in some specimens, the capitulum being longer by one-fifth of
its total length than broad; in others, one-fifth broader than long.
Valves generally approximate; in some varieties, however, from the
narrowness of the carina and terga, the valves stand far apart, there
being an interval between the carina and scuta of nearly half the
breadth of the latter. Valves excessively thin, brittle, transparent,
colourless, smooth, but generally sinuous along the zones of growth,
which are conspicuous: valves generally covered throughout by thin
chitine membrane, which is thickly clothed, especially in the
interspaces between the valves, with minute spines, barely visible to
the naked eye. _Scuta_ with the lower part of the tergo-carinal margin
extremely protuberant; occludent margin, more or less, but slightly
reflexed, with a depressed line running from the umbo to the apex; basal
margin much reflexed, but to a variable extent and at a v