CHAMA. 55 



shells with equal and with unequal valves, 

 shells fixed to other marine bodies, with those 

 that are free ; some with one, others with ttvo 

 muscular impressions. In the present genus, 

 Chama, the shells are irregular, thick, scaly, or 

 spinous. The hinge has one thick tooth, often 

 notched : the beaks are bent inwards. They are 

 found in the Indian, American, and Mediterra- 

 nean seas. There are several fossil species. 



'' The first order, Bimuscidosa, is finished. 

 In our next lesson we shall proceed to the fami- 

 lies and genera contained in the second, Uui- 

 muscidosa," 



