Venerid^.- 



-MOLLUSCA.- 



-CVCLADID.E. 



361 



larly lieart-shapeil ventricose shell, with three com- 

 pressed, erect teeth in the hinge in each valve. The 

 margins of the shell, internally, are finely crenulate, 

 and the pallial sinus is short, narrow, triangular. There 

 are only four species described, all from the American 

 Eoas. The hinder margin of the inner surface of each 

 valve of one species {Af. violacea) is of a fine deep violet 

 colour ; and, as already mentioned, it is this shell which 

 the Red Men in America regard with so much interest 

 and use as trampiim. 



Genus Chione. — This genus has an ovately triangu- 

 lar, somewhat thickened shell, with the margins finely 

 crenulated. Tlie hinge is solid and provided with three 

 teeth in the right, and two in the left valve. The 

 external ligament is narrow, and the pallial sinus is 

 nearly obsolete or very short and triangular. The sur- 

 face of the shell in this genus, which varies a good deal 

 in form, is lamellated, cancellated, smooth, or trans- 

 versely striated. 



Genus Tapes. — This genus consists of oblong shells, 

 with the hinder end the longest, the margins eraooth, 

 and the hinge provided with three compressed, slightly 

 diverging cardinal teeth in each valve, two of which 

 are usually bifid. The pallial sinus is deep and rounded. 

 The foot of the animal in this genus occasionally spins 

 a byssus, by which it secures itself when it is in danger 

 of being carried away. " The Tapes puUastra, which 

 is usually free — for I have often found it so, and never 

 moored, if placed in a situation where it would be liable 

 to be carried away by the current — averts the fatal wreck 

 by attaching itself by some filaments to the shingle or 

 stones around it." — Johnston. 



Genus Venerupis, or the Venus of the Uoch. — 

 This genus has an oblong shell, gaping a little pos- 

 teriorly, and a hinge with three small teeth in each 

 valve, one of them being bifid. The pallial sinus is 

 moderately deep and angular, and the surface of the 

 shell is radiately striated and ornamented with con- 

 centric lamelloe. The species are generally found in 

 crevices of rocks, and are said to possess the power of 

 perforating the limestone or challi, &c., in which they 

 are lodged. Mr. Rang admits this power, and says that 

 when they have reached their adult state they cannot 

 get out of the cavities they have made, " the aperture of 

 the excavation being too small to admit of their egress," 

 Jlr. Sowerby, however, thinks that the cavities in 

 which these shells live " are rather the natural conse- 

 quence of the action of the sea-water in conjunction 

 with some of the excretions of the animal upon the 

 chalk or limestone, than of any power of the animals 

 themselves to pierce independently of such action." 

 Sowerby, however, here confuses the two genera Tapes 

 and Venerupis, while Rang strictly confines the genus 

 Venerupis to those species which really do bore. 

 Several other genera belong to this family ; but as the 

 species in each are few, we must pass them over and 

 proceed to the next. 



Family— CYPRIXID^. 



This family consists of substantial, thick shells, 

 invested with a strongly developed epidermis. They 

 are ovate-cordate, with prominent incurved beaks, no 



Vnl. IT. 



lunule, and smooth margins. The hinge is furnished 

 with three cardinal teeth, and one lateral tooth in each 

 valve. The ligament is external, thick, elongated ; 

 and the pallial line is simple. 



Genus Cyprina. — Tliis genus is the only one known, 

 and there is only one species in the genus. The C. 

 islanelica is one of the largest of our British shells, and, 

 besides, is common to European and North American 

 seas. It ranges, indeed, from Greenland and the United 

 States to the Icy sea. It is said to be carnivorous in its 

 habits, and Dr. Johnston tells us that it often swallows 

 the bait of the fishermen. He found in the stomach of 

 an individual the indigested remains of a large green 

 Nereis. 



Family— GLAUCONOMID^. 



This family is by many authors placed amongst the 

 VeneridcB. 



Genus Glauconome. — This is the only one. In it 

 the shell is oblong-oval, thin, and covered with a hard, 

 olive-green epidermis extending beyond the edge of the 

 valve. The hinge is narrow, and furnished with three 

 cardinal teeth in each valve, one of which is bilid. The 

 ligament is external, marginal, and the pallial sinus is 

 very deep and angular. The species of this genus are 

 all natives of the mouths of rivers, even where the 

 water is partially fresh. They appear to be exclusively 

 confined to the Philippine Islands and Indian seas. They 

 live buried in the sandy mud of the estuaries, and 

 appear to be very similar in their habits of life to the 

 Sulcus or Razor-fish. 



Family— PETRICOLID^. 



The Petricolas have an ovate-elongated, thin, tumid, 

 gaping, often irregular shell, which is usually white, or 

 covered with a thin, hard epidermis. Tlie hinge is 

 narrow, and has two cardinal teeth in each valve, 

 which are bent up as if coming from the inner surface 

 of the shell under the umbo. The pallial sinus is deep 

 and rounded. The species of this family are generally 

 found burrowing in limestone and coral rocks, and 

 stones, or in mud; and appear to be most numerous in 

 Western America. 



Family— CYRENID^ (= CorhkuMas.—Gr&y). 



The Cj'renas have a rather tumid, suborbicular shell 

 covered with a hard, brittle, often polished epidermis 

 and a hinge composed of two or three, sometimef 

 diverging, cardinal teeth in each valve, and two com- 

 pressed lateral teeth, which in some cases are trans- 

 versely striated. The shell is solid, the beaks oftcr 

 eroded, and the surface of the valves is concentrically 

 furro%ved or striated. The pallial line is only slightly 

 sinuatcd. This family consists of fresh-water shells 

 and is numerous in species. The genera are Corbicula, 

 Batissa, and Cyrena. 



Family— CYCLADID>^. 



The Cyclases have been separated from the Cyrenicla 

 because the animals slightly differ. The shell is Ihiii, 



2 Z 



