CONCHIFERA. 



317 



Plicatula. Lam. (Harpax Parkinson.) — Shell ir- 

 regularly ovate, inequi valve, one valve being 

 more convex than the other, sides strongly 

 and transversely grooved ; ligament internal, 

 between the teeth ; bosses unequal. Animal 

 unknown. — 7 species ; also fossil. 



Attached by the under valve to stones and 

 rocks. They are brought from the Indies, and the Philip- 

 pines, and Sowerby says the grooved teeth lock so firmly 

 into each other that the valves cannot be separated with- 

 out breaking them. 



Sph^ra. Sow. — Shell globose, eared ; with one cen- 

 tral, and two (?) remote teeth about the hinge ; ears ob- 

 tuse, short, incurved ; the line of the hinge is long, slightly 

 curved, and terminated at one, perhaps at both ends, by a 

 flat obscure tooth, beneath the commencement of the ear ; 

 in the centre of it is a large irregular tooth, transversely 

 flattened and turned towards the incurved beak ; the shell 

 is thick, and very gibbose.* — Fossil. 



Only 1 species known, S. corrugata. 



Family 4. — OSTRA CEA. 



The animal has the mantle entirely cleft, with a thickly 

 fringed edge ; no distinct foot ; large, curved, almost equal 

 gills ; two pair of lengthened lance-formed mouth ten- 

 tacles. The shell is irregular, foliaceous ; the under- valve 

 mostly attached. The Ostracea are not found in the seas 

 of the frigid zone. 



Ostrea. Lin. — Shell inequivalve, irregular, substance 

 foliaceous or in loose layers ; bosses distant, and very un- 



* Sowerby 's Mineral Conch. 



