84 CONCHOLOGY. 
ous; inferior valve a little flatter than the superior, divided at the 
summit into two sloping branches, whose approximation forms a 
large oval hole ; the superior valve, which is the larger, has an 
oval excavation under the summit ; a subcentral muscular impres- 
sion, divided into three parts. Inhabits the British coasts. Two 
beautiful species are found on the shores of Rhode Island and 
New Jersey. Nine species. 
Anomia patellaris. Anomia cepa. 
A. pyriformis. A. electrica. 
A. lens. A. membranacea. 
A. squamula. 
—_— 
A ephippium.* A. fornicata.* 
6. Genus Crania. Pl. IX. 
Animal, See Anomia. 
Shell. Orbicular, the upper valve gibbous and conical; lower 
valve, fiat, with three perforations. Inhabits the Indian Ocean. 
One species. 
Crania orbicula. 
FAMILY XX. 
Bracuwioropa. Three genera. 
1, Genus Orbicula. Pl. IX. 
Animal. Body much compressed and rounded; mantle open 
throughout its whole circumference; two ciliated tentacular ap- 
pendages. 
Shell. Orbicular, much compressed, inequilateral, very inequi- 
valve ; inferior valve very thin, adhering, imperforated, the superior 
patelloid, with the summit more or less inclined towards the 
posterior side. Inhabits the Norwegian seas. One living species. 
Two fossil. 
Orbicula Norwegica. 
2. Genus Terebratula. Pl. IX. 
Animal. Depressed, circular or oval, more or less elongated, 
with two, long, pectinated, labial tentacula. 
