44 Lamarck's Genera of Shells. 



associated the beautiful genus of the pectines, with that of the 

 ostrese, notwithstanding the former are free, regular shells, and 

 have the ligamental pit wholly internal. He, moreover, referred 

 some true ostrese to his mytili, viz., mytilus crista r/alli, mytilus 

 hyotis, and mytilus frons ; and added the whole genus perna, to 

 the ostreffi, although their hinge is so peculiar by its charac- 

 teristic indented line. Bruguiere first established the principal 

 limits of this genus, and Lamarck has since further reduced 

 them, by separating the vulsella, podopsis, and gryphoea. 



The shell of the ostrea is rude, rugged, often squamose, some- 

 times singularly plicated at the margins, and frequently very 

 thick. It does not curve upwards, like that of the gryphoea. 

 The texture of the valves- is loose-foliated ; the lower one, which 

 is the largest, and by which it adheres to marine bodies, is more 

 convex than the upper. 



The species are subdivided into (1) shells, with simple, or 

 wavy margins, but not plicate — 32 species; and (2) those with 

 distinctly phcated margins — 16 species. 



Type. Ostrea eduUs *. (Idem. Lin7i.) 



Shell ovate-rounded, base sub-attenuated; membranes imbri- 

 cate, wavy; upper valve flat. European seas. In all 48 recent 

 species, and 33 fossil. PI. II. Fig. 94. 

 8. Vulsella t. 



Shell longitudinal, subequivalve, irregular, free; beaks equal. 

 Hinge with a prominent callus on each valve, depressed above, 

 with the impression of a conical, obliquely arched pit, for the 

 ligament. 



The vulsellae, though nearly allied to the ostrese, are distin- 

 guished from them, by having the valves always of nearly equal 

 size ; the beaks equal, though somewhat separate ; an equal, 

 projecting callus in the interior of each valve, under the beaks ; 

 and by the shell never being fixed by its lower valve. They are 

 often found in spc nges ; are pearly internally, and some species 

 gape a little at the posterior side. 



Type. Vulsella spongiarum J. 



; * Eatable. t Or \o\se\lai— tweezers. 



; 1 Of spunges. Lamarck's 4th species. His type is V. Ungvlata. 



