196 



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

 fossil. — PI. 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. — PI. 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. — PI. 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. — PI. 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 — SphemditeSi Radiolites, Calceola, 

 Birostrites, Discina, and Crania. 



1. Spherulites. — An unequal valved, orbiculato-globcse 

 bivalve, a little depressed at the top ; outwardly echinated 

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



