74 TESTACEA. 



Plate XV. 



Fig. 3, 4, 5. Pholas crispata, shell. 



6. Specimen extended. 



7. Pholas dacti/lus. 



Plate XVI. 



Figs. 1-10. Pholas crispata. 



9. Pecten— r/i? Scallop.— V\&iQ XVII., Figs. 1, 2, 3, 4. 



This is a numerous genus of bivalves, comprehending subjects much 

 varied in dimensions, form, and colour, vrhich could be specified only by 

 long enumeration. 



There seems a general resemblance to predominate among the ani- 

 mals dwelling in the shells, which, without sufficient authority, have 

 been compared to the Tethys, one whose nature is little understood. 



The shells of all are flattened, thin, and light. Some at least three 

 inches in diameter, down to very small dimensions ; with two ears at the 

 hinge, equal or unequal in relation to each other. The surface of the 

 shell radiates in Uutiugs, from about the hinge down to the circumference. 



Pecten opercitlaris. — Plate XVII., Figs. 1, 2, 3. 



This shell attains three inches in diameter ; it is of fattened form : 

 one ear somewhat less than the other. The ribs or rays exceed twenty ; 

 they are about twenty-three ; convex above, hollow below, that is within 

 the valve. Colour dingy white, or variegated vivid red and white. The 

 animal appears thick as the valves open ; its circumference is studded 

 with a numerous row of resplendent green ocelli on each lobe. Nume- 

 rous long tentacular organs likewise issue from the margin, with many 

 interior short fibrilli, like slender teeth, directed inwards. A short white 

 foot protrudes from the shell, which seems to aid smaller specimens only, 

 to their position. 



