Lnmarck's Genera of Shells. 4^ 



species, the shell is fixed to marine bodies by the lower valve, 

 which is always the largest. The first three genera of this 

 family have a semi-internal ligament, a foliated, and often very 

 thick shell. The two last have the ligament internal, and the 

 shell thin or papyraceous. 



1. Gryphoea *. 



Shell free, inequivalve; lower valve large, concave; beak 

 prominent, curved spirally inwards ; upper valve small, flat, 

 opercular. Hinge without teeth ; cardinal pit oblong, arched. 

 A single muscular impression on each valve. 



Animal unknown. 



The generally large curved beak of the lower valve of the 

 gryphoea, usually projects considerably, either above the upper 

 valve, or laterally, which eminently distinguishes these shells 

 from the ostrese ; they are, besides, almost always free shells, or 

 if they adhere at all to other bodies, it is only by a point ; most 

 of them appear to be regular shells. The lower valve is always 

 much larger than the upper. They are all, but one species, 

 fossil, and are probably sea-shells. 



Type. Gryphcea angulata t. 



Shell oblong ovate ; three longitudinal ribs underneath, angu- 

 lar-carinate; beak large, suboblique. Recent. Locality not 

 given. 



11 Fossil species. PI. II. Fig. 93 J. 



2. Ostrea §. 

 Shell adhering, inequivalve, irregular, beaks distant, becoming 

 very unequal by age ; upper valve smallest, generally flat, and 

 gradually advancing forward, during the life of the animal. (See 

 note *, p. 41.) Hinge without teeth. Ligament semi-inter- 

 nal, inserted in the cardinal pit of the valves ; pit of the lower 

 valve increasing by age, sometimes to a great length. 



Linnaeus, looking only to their mutually being without teeth, 



• From j/{U7r«c, one that lias a hooked nose. ^ Angular. 



i We have given a second figure of this genus, viz., G. Cymbium, (fossil, 

 fig. 93 •,) the (J. mifruUUa, being.very rare and less characteristic of the spe- 

 cies usually found in the blue lias, &c. 



II Oyster. 



