19G 



hinge-pit oblong and bowed ; one impression. Recent and 

 fossil. PL vii. fig. 1. 



Le Chev. de Lamarck states his having seen, at Paris, 

 one species in a recent state. 



2. Ostrea. An adherent, inequivalved, irregular bivalve, 

 the beaks disjoined ; the valves becoming more unequal with 

 age, so 'that the upper valve is gradually protruded; the 

 hinge is toothless ; the ligament semi-internal, affixed in the 

 hinge-pit, which, in the lower valve, increases with the beak 

 to a considerable length. Recent and fossil. PL vi. fig. 29. 

 3. Vulsella. A long, subequivalved, irregular, free bi- 

 valve, with equal beaks ; the hinge having, upon each valve, 

 a projecting callosity, with a conical ligamented pit obliquely 

 bowed. Recent and fossil. PL vii. fig. 4. 



4. Placuna. A free, irregular, flat, subequivalved bi- 

 valve ; the hinge has interiorly, on one valve, two longi- 

 tudinal sharp ribs, approximated at their base, and diverging 

 in the form of a V ; and, on the other, two corresponding 

 depressions ; at this part the ligament is attached. Recent 

 and fossil. PL viii. fig. 5. 



5. Anomia. An unequal valved, irregular, operculated 

 bivalve, adherent by its operculum ; one valve, which is 

 pierced, is generally flat, having a hole or notch at its base ; 

 the other, a little larger, whole and concave ; the operculum 

 is small, elliptical, and subosseous, and is affixed to various 

 marine bodies. Recent and fossiL PL vii. fig. 10. 



Under the designation les rudistes, Lamarck places those 

 shells in which neither the hinge, the ligament of the valves, 

 nor the muscle of attachment, is discoverable : these he 

 places under six genera Spherulites, Radiolites, Calceola, 

 Birostrites, Discina, and Crania. 



1. Spherulites. An unequal valved, orbiculato-globose 

 bivalve, a little depressed at the top ; outwardly echinated 

 with large subangular scales ; the upper valve small, oper- 



