GENUS XV. ANOMIA. 81 



Lamarck has divided this genus into seven, as follow : 



GrtphjEa. Shell with unequal valves, the lower valve con- 

 cave, terminated by a beak, curved upwards and inwards, 

 the upper valve much smaller, like an operculum ; the 

 hinge toothless, the hollow or pit oblong and arched ; one 

 muscular impression in each valve (see Anomia Gryphiis, 

 /. 45). 



Placuna. Shell free, flat, with equal valves; the hing-e with 

 two longitudinal teeth or ribs on the interior surface of 

 one valve diverging, or in form of a V ; and on the other 

 valve two corresponding hollows which serve for the at- 

 tachment of the cartilage (see Anomia Placenta, f. 46). 



Anomia. Shell irregular, with unequal valves, the lower valve 

 perforated near the b eakw hich aperture is closed with 

 a little bony operculum attached to a cartilage passing- 

 through the hole or notch, and serving to fix it to other 

 bodies (see Anomia Ephippium, f. 47). 



Crania. Shell inequivalved, the lower nearly flat and round, 

 pierced on its inner face with three unequal and oblique 

 holes ; the upper valve very convex, furnished on the in- 

 terior surface with two projecting callosities (see Anomia 

 craniolaris, Chemn. 8. t. 7G. f. 687). 



Terebratula. Shell regular, fixed by a ligament or short 

 tube; the valves unequal, the larger of which has the 

 beak produced and pierced with a hole, through which 

 the ligament passes ; the hinge with two teeth. Two thin 

 branching bony rays projecting inside from the valve 



M 



