52 



POPULAR CONCHOLOGY. 



dinal processes nor any hinge. — 1 recent and 

 4 fossil species. 



From the Indian seas. (Lamarck.) 



5. Orbicula. — Shellhomy, orbicular, rather 

 irregular, inequivalve, rather compressed, the 

 upper valve like a patella, the 

 lower flat. In the centre of the 

 latter is a small oval depression, 

 with an oblique fissure in it for 

 the passage of a tendon; four 

 muscular impressions in each 

 valve. There is no hinge. Ani- 

 mal having two short ciliated arms.— 4 recent 

 and 2 fossil species. 



These shells are found in the Northern Seas, 

 and those of Peru and Chili. The species from 

 Peru is very abundant, the individuals are 

 grouped one on the other, and form large 

 masses. 



