195 



the hinge with two strong teeth on each valve, with a pit 

 between receiving the hgament, w^hich is entirely external. 

 Recent and fossil. — PI. viii. fig. 4. 



The shell, named harpax, in Organic Remains, Vol. iii. 

 and figm*ed, PI. xii. fig. 14, 15, 16, 17, and 18, differs from 

 plicatula of Lamarck, in being an attached shell, and in 

 having its teeth not disposed like those of spondylvs, hxxt in 

 the form of a V, and in their being crenulated. It appears 

 to agree, in its specific properties, with P. tubifera of 

 Lamarck. 



6. Spondylus. — An unequal valved, adherent, eared 

 bivalve, rough or echinated ; the beaks unequal ; the lower 

 valve having a flat external cardinal area, divided by a 

 groove ; the hinge has two strong teeth on each valve, with 

 an intermediate pit for the ligament, communicating by its 

 base with the outer groove ; the ligament internal. Recent 

 and fossil. — PI. viii. fig. 6. 



7. Podopsis. — An unequal valved, subregular bivalve, 

 not eared, adhering by the beak of its lower valve ; the 

 lower valve is larger and more convex than the upper, and 

 has its beak more advanced ; the hinge is without teeth, and 

 the ligament internal. 



These shells are only known as fossils : the upper valve 

 has no curved or projecting beak, nor is the lower beak re- 

 curved over the upper valve, as in gryphcea. They more 

 resemble the pectens in the regularity of their forms and 

 their longitudinal striae. 



Ostracece. — The ligament internal or semi-internal ; the 

 shell irregular and foliaceous, or even, sometimes, papy- 

 raceous. 



1. Grypha^a. — An unequal valved free bivalve, the in- 

 ferior valve large and concave ; the beak large, incurved, 

 and terminating in an involuted spire ; the upper valve small 

 and flat, like an operculum ; the hinge edentulous ; the 



