112 CONCHIFERA. DIMYAIRA. 



** Primary teeth a little distant from the anterior margin. 



S. pygmceus, Lam. (S. pellucidus, Pen.) Shell linear, somewhat 



curved ; hinge with a double tooth in one valve,, and one in the 



opposite; epidermis strong, pale greenish brown. -J- inch long, and 



1 inch broad. Shores of Britain. Pen. Brit. Zool. iv. pi. 49, fig. 2. 



S. cultellus, Lin. Shell linear, oval, somewhat curved ; hinge with 

 two teeth in one valve, and one in the other ; thin, brittle, whit- 

 ish, with tawny spots, but often covered with a brown epidermis, 

 and marked with fine concentric striae. | inch long, and four 

 times as broad. Shores of Indian seas Wood's Conch, pi. 29, fig. 2. 



* * * Hinge nearer the middle than the anterior end. 

 S. legume?) } Lin. Shell linear, ovate, straight ; hinge placed in the 

 middle, with two teeth in each valve and one of them bifid j thin, 

 subpellucid, white, with a yellowish epidermis. Three quarters 

 of an inch long, and more than four times as broad. Inhabits Eu- 

 ropean coasts. B. Pen. Brit. Zool. iv. pi. 49, fig. 3. 



S. radiatus, Lam. Shell oblong-oval, straight, violet, with four white 

 rays ; hinge with two teeth in each valve, and a strong white de- 

 pressed rib extending somewhat obliquely along the inside of the 

 shell. Inhabits Indian Ocean. Wood's Conch, p. 31, fig. 1, 2. 

 A fossil species of this genus has been found in the London clay. 



FAMILY III. PHOLADARIA. 



Shell bivalve, with accessory pieces to the valves; or gaping much 

 anteriorly. 



The animals of this family are borers, and burrow in calcareous rocks, wood, 

 masses of madrepores, &c. Their shell is generally thin, whitish, and rough, with 

 transverse waved striae. They bore by the rotatory motion of their shell, which is 

 broadest posteriorly, and enlarge their habitations downwards as the animal increases 

 in size. 



Gen. 53. GASTROCHCENA. 



Shell bivalve, equivalve, almost wedge-shaped ; with the ante- 

 rior opening very large, oval and oblique ; hinge linear, mar- 

 ginal, without teeth. 



G. cuneiformis, Lam. (Pholas hia?is, Chem.) Shell wedge-shaped, 

 slender, subpellucid, with transverse arched striae. ^ inch long, 

 and thrice as broad. Inhabits Indian and American seas. Chem. 

 x. pi. 172, fig. 1678, 1681. 



G. modiolina, Lam. (My a dubia, Pen.) Shell small, very fragile, 

 with the beaks nearly terminal, and rather prominent. \ inch 

 long, and 1 inch broad. Inhabits European coasts, in limestone. 

 Penn. Brit. Zool iv. pi. 47- 



Gen. 54. PHOLAS, Lam. Lin. 



Shell bivalve, equivalve, transverse, gaping on each side, with 

 several accessory pieces either on the hinge or below it ; in- 

 ferior margin of the valves bent outwards ; animal destitute 

 of a tubular sheath, projecting anteriorly two united tubes, 



