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BIVALVES. SPONDYLUS. 



SPONDYLUS.— Thorny Oyster or Artichoke- 

 head. 



Animal— a Tethjs: Shell hard, solid, luith unequal valves; 

 one of the valves convex, the other ralhcr fat: hinge 

 with two recurved teeth separated by a small holloiv. 



This genus, though contaming innumerable varieties, is 

 divided into no more than four distinct species, and even 

 these, from their extreme irregularity of formation, and 

 great difference of appearance, are often confounded with 

 each other. However, the usual character of the Spon- 

 dylus is to have its valves something similar to those of 

 the common oyster, viz. one convex, the other a little 

 flattish, having their outsides covered with longitudinal 

 rows of erect spines or ramifications. The spines are 

 usually tubular or round, ending in a point; the ramifi- 



