cond
pair. Second cirrus, with its anterior ramus shorter by two or three
segments than the posterior ramus, and thicker than it, with the
segments covered like brushes with bristles; posterior ramus, and both
rami of the third cirrus, a little more thickly clothed with bristles
than are the three posterior cirri.

_Caudal Appendages_, minute, broadly oval, with six or seven long
bristles on their summits.

_Genus_--CONCHODERMA. Plate III.

CONCHODERMA. _Olfers._ Magaz. der Gesellsch. Natuforsch. Freunde
zu Berlin, Drittes Quartel, 1814.[34]

LEPAS. _Linnaeus._ Systema Naturae, 1767.

BRANTA. _Oken._ Lehrbuch der Naturgeschichte, Th. 2, p. 362, 1815.

MALACOTTA et SENOCLITA. _Schumacher._ Essai d'un Nouveau Syst. des
Habitations des Vers., 1817.

OTION et CINERAS. _Leach._ Journal de Phys., vol. lxxxv, p. 67,
July, 1817.

GYMNOLEPAS. _De Blainville._ Dict. des Sci. Nat., Art. Mollusca,
1824.

PAMINA. _J. E. Gray._ Annals of Philosophy, vol. x, (Second
Series,) August, 1825.[35]

[34] The general title to the volume, containing four Quarterly
parts, is dated 1818; but as in the 'Journal de Physique,' for
July, 1817, the editor refers to Conchoderma, the Quarterly Part
containing this genus must have appeared before 1818: Lamarck
gives the year 1814 as the date of the paper in question, and I
have accordingly followed him. From a similar reference by the
editor, it appears that Schumacher's volume appeared before the
number of the 'Journal de Physique' containing Leach's Paper.

[35] Under these nine generic names, the two common species of
Conchoderma have received thirty-three different specific
denominations, caused partly by changes of nomenclature, and
partly from varieties having ranked as species.

_Valvae 2 ad 5, minutae, inter se remotae: scuta bi-aut tri-lobata,
umbonibus in medio marginis occludentis positis: carina arcuata,
terminis utrinque paene similibus._

Valves 2 to 5, minute, remote from each other: scuta with two or three
lobes, with their umbones in the middle of the occludent margin: carina
arched, upper and lower ends nearly alike.

Filaments seated beneath the basal articulations of the first pair of
cirri, and on the pedicels of four or five anterior pairs; mandibles,
with five teeth, finely pectinated; maxillae step-formed; caudal
appendages, none.

_Distribution._--Mundane, throug