The gills have the same laminated structure as that observed iu other bivalves, they aro broad and short, corresponding to the form of the animal ; and the laininre, not thin compressed layers, but broad and projecting but little from the sides of the visceral mass, are arranged in three layers instead of two, on either side of the foot.
The digestive system is accordant with the structure of the same part in the other acephaloila mollusks. The mouth, a transverse slit, without masticatory or salivary organs, is bounded by the upper and lower labial processes which are continued in the form of two transversely striated pointed tentacles on either side : these prehensile, sensitive, and probably respiratory organs measure each six lines in length, and about one and a half lines in breadth. The (esophagus, after a course of two lines, dilates into a stomach, the sides of which are perforated by the large hepatic ducts. The intestine, after a course of eight lines, forme,' small (mecum about one line in length. The intestine, after making three close turns upon itself in the mass of era and hepatic follicles at the base of the foot., passes in imme diate contact with but not through the heart, and then below the posterior adductor, to opposite the posterior orifice of the anal tube. The exterior of the intestine has an irregular honey-combed appear ance, from the close adhesion to it of the capsules of the ova. The liver has the Ramo divided follicular structure and green colour as in the other Bivalves.
The nervous system consists of it large and conspicuous ganglion aituated at the posterior part of the base of the foot, just above the orifice of the anal tube. Two nervous cords extend front this ganglion, on either side the foot, to the month; other branches radiate in the opposite direction to the aiphonic and adductor muscles.
The ovary, of a gray colour, forme a mass at the dorsal aspect of the body above the great adductor muscle, and extending ventral on either side the (esophagus and stomach to the opposite end of the base of the foot. All this mass of intestinal folds, hepatic) follicles, and ova was covered by a thin membrane. The little muscular process or foot which passes through the anterior slit of the mantle is but four lines long, and half a line in breadth : its possible use may be to apply a solvent to tho rock in which the chamber is excavated.
Mr. Broderip observes that we are left to conjecture the causes which operate to determine the animal in the choice of its abode, if indeed it can be called choice, for most probably Clarayella is the creature of circumstances, and if, soon after its exclusion from the parent (when Mr. Brodcrip supposes it to be furnished with its two
Fig I, part of calcareous grit rook containing the fixed valve and part of the tube of leis ; 3, external view of the right or free valve; fig. 1, internal view of the same, showing the muscular impressions corresponding with those of the left or fixed valve ; fig. 2, soft parts of a lain seen from the right side, the dermal layer of the mantle, e, being removed ; fig. 5, the same seen front the left side, or that which Is in contact with the fixed valve. The extremities of the left labial appendages only are exposed, no part of the gill being pro truded. A bristle is placed In the opening of the mantle, a, anterior wall of the chamber ; 5, dorsal wall, the letter pitent on the hinge of the fixed valve ; e, ventral wall ; d, posterior or siplionle outlet ; e, tubular communisations with a neighbouring cavity, here sent off from the posterior part of the mantle ; e calcareous tofu,' secreted by the above proccases and extending into the cavities contiguous to the throat of the lobe; sr', • cavity communicating with the anterior part of the chamber; impression of the posterior adductor muscle; g', Impressioa of the anterior adductor muscle; A', Impreeslanot (be pallial muscle, or third adductor ; f, posterior ur large adductor (the single adductor of the Oatrarea, 4c„, corresponds to this, the following arc super added in other families of Bivalves); 9, the anterior, antero-dorsal, or smaller adductor; h, the palliat or antero-ventral adductor ; i„ the convex muscular Huss continued over the anterior part of the body, and reducing the opening of the mantle to the small alit', through which a bristle Is placed in fig. 5 (this mass is en Inordinate development of what forms the muscular margins of the mantle lobes In other Bivalves) ; k, muscular fibres of the siphon ; 1 (fig. 6), the respiratory, or Ingestive slphonle canal; at, the anal or cgestive siphonic canal; n, the labial or buccal appendage; t, tbo gills: in fig. 2 the right gill is seen partially protrudmi between the muneubsr parts of the mantle; r, part of the ovary (figures and description from Owen, to whose lucid memoir and illustrations the render is referred for the anatomy of the internal parts) ; fig. 7, anterior termination of the ebony tube of C. sperms, Sow., from Mr. Sowerby's Genera of Recent and Fossil Shells.