_Animal._ Body pedunculated, enveloped in a membranous tunic, which is ventricose above; two horn-like tubes, directed backwards, truncated, and open at their points, and situated in the apex of the tunic; having a lateral opening, with many articulated and ciliated arms. _Shell._ Composed of two testaceous valves, attached near the lateral opening, the centre aperture admitting the animal’s tentaculæ, the singular form of which prevents its being blended with the genus cineras without a further examination of its structure. Inhabits the North seas. Two species. Otion Cuvieri. O. Blainvillii. CLASS III. CONCHIFERA. _Animal._ Soft, inarticulated, always fixed in a bivalve shell, without head or eyes, having the mouth naked, concealed, and without any hard parts; a large mantle enveloping the whole of the body, forming two laminiform lobes; the edges detached or sometimes united in front. Gills or respiratory organs external, situated on each side between the body and the mantle; circulation simple, the heart with one ventricle; some few ganglions of the different nerves, but no knotted medullary cord. _Shell._ Always bivalve, enveloping the animal entirely or partially, sometimes free, sometimes affixed; the valves most frequently united on one side by a hinge or ligament. Sometimes attached to the shell are testaceous accessory pieces. Twenty families. FAMILY I. TUBICOLA. Six Genera. 1. Genus _Aspergillum_. Pl. V. _Animal._ Entirely unknown. _Shell._ Oval, somewhat elongated, striated longitudinally, conic, club-shaped, having two valves incrusted on one side of the club, open at its attenuated extremity, and terminated at the other by a convex disk, pierced by a number of small perforations, and encircled by a dilated margin of papyraceous tubes, resembling a plaited ruff—smaller extremity always open. This is a well known, but rare shell, found in sandy places in low water in the Indian ocean. Four species. Aspergillum Javanum. A. vaginiferum. A. Novæ Zælandiæ. A. agglutinans. 2. Genus _Clavagella_. Pl. VI. _Animal._ Unknown. _Shell._ A tubular sheath, testaceous, attenuated, and open before; terminating posteriorly in an oval, sub-compressed club, roughened by spiniform tubes—one valve fixed in the side of the club, the other free in the tube. Inhabits the Indian seas. Four species. Clavagella aperta. C. cristata. C. tibialis. C. Brocchii. 3. Genus _Fistulana_. Pl. VI. _Animal._ Provided with two protuberant calcareous tubes, covering parts of its body at the open end of the tube, each of which is terminated with from five to eight cup-shaped calcareous or corneous appendages. It inhabits the sand, and perforates wood, stones, and sometimes shells.