SPONDYLUS THORNY OYSTER. 167 



VENUS Dysera* 

 RIBBED VENUS. 



Specific character. Shell triangular, convex, 

 heart-shaped, marked with distinct concentric 

 raised ridges, which are closely cancellated ;f 

 the longitudinal striae are also crossed by fine 

 transverse lines ; margin crenated ; colour gray, 

 or ivory white, variously marked with chestnut 

 brown spots, the area and areola are of the same 

 colour as the spots ; diameter about an inch. 



Found on the shores of Germany, America, 

 and the East Indies. 



GENUS. SPONDYLUS. J ' 



THORNY OYSTER. 



Generic character. Shell bivalve, inequivalve, 

 inequilateral, fixed, strong, solid ; surface coarse 

 and rough, with either lamellar or subulate 

 spines, or ramifications ; the hinge has two 

 strong recurved teeth in each valve, with an 

 intermediate sinus for the ligament; the lower 



* Plate VIII. figure 8. 



f Cancellated, crossed like the bars of a window, from the Latin 

 cancelli, lattice. 

 I Plate VIII. figures 9, 10. 



