224 PHOLAS. 



operculum, we may regard it as well defined ; but there are some 

 spirally-grooved species of Turbo, Linn, which, from their oval 

 shape, have been considered as belonging to this genus. Such 

 species should not, in our opinion, be retained in this genus ; 

 they belong to Littorina. P. variegata, fig. 367. 



PHITIA. Gray. Carychium, M tiller. 



PHOLADARIA. Lam. A family of the order Conchifera Dimy- 

 aria, Lam. The animals contained in this family live in cavities 

 bored by themselves in rocks, wood, &c. They are cylindrical 

 in form. Lamarck here places Pholas and Gastroch.ena, the 

 last of which belongs more properly to the family of Tubicolaria, 

 where we have enumerated it. Pholas has been divided into 

 Pholas, fig. 55, Martesia, which has the valves nearly closed ; 

 and Pholadidaea, fig. 56, which has the cup -shaped extension. 

 The genus Pholadomya, fig. 67, has been added, although of 

 doubtful character. The genus Galeomma, fig. 58, 59, has also 

 been recently added. 



PHOLADIDiEA. Leach. Pholas papyracea, Auct. Remarkable 

 for the cup-shaped process at the posterior extremity. Fig. 56. 



PHOLADOMYA. Sow. (Pholas and My a.) Fam. Pholadaria, 

 Lam. — Descr. Thin, rather hyaline, equivalve, inequilateral, 

 ventricose, posteriorly gaping, elongated, anteriorly short, round- 

 ing ; ventral margin rather gaping ; hinge with an elongated 

 pit, and lateral plate in each valve ; ligament external, short, 

 muscular impressions two in each valve, rather indistinct ; palleal 

 impression with a large sinus. — Obs. The only recent species of 

 this genus is from the island of Tortola. Several fossil species 

 occur in rocks of the Oolitic series. Fig. 57, P. Candida. 



PHOLAS. Auct. (®(x)\eu), pholeo, to lie hid in a cavity.) Fam. 

 Pholadaria, Lam. Adesmacea, Bl. —Descr. Transverse, oblong, 

 equivalve, inequilateral, imbricated, gaping on both sides, the 

 anterior hiatus being generally the largest, although sometimes 

 nearly closed, with the dorsal margin surmounted with one or 

 more laminar accessary valves ; hinge callous, reflected, with a 

 long curved tooth protruding from beneath the umbones in each 

 valve. — Obs. This genus of marine shells, dwelling in holes 



