BIVALVES, — SPONDYLUS. 53 



Undulata — Undulated. *Perforans — Piercing. 



Obsoleta — Obsolete. Virginea — Virgin, 



*Decussata — Intersected. *Aurea — Golden. 



Senegalensis — Senegal. *Palustris — Marshy. 



Monstrosa — Distorted. 



Family 2. — Foliated. 

 Agaracoides — Mushroom. 



SPONDYLUS.— Thorny Oyster. 



Animal — a Tethys: Shell bivalve, solid, tvithunequal valves: 

 one of the valves convex, the other rather fiat; hinge with 

 two recurved teeth separated hij a small hollow. 

 THIS genus, though containing innumerable varieties, 

 is divided into no more than ten species, and even these, 

 from their extreme irregularity of formation and great simi- 

 larity of appearance, may often be confounded with each 

 other. However, the most striking character of the Spon- 

 dylus is, that its valves, which resemble those of the com- 

 mon oyster, viz. one convex, the other rather flat, have 

 their outsides covered with longitudinal rows of erect spines 

 or ramifications. The spines are usually tubular, ending 

 in a point; the ramifications or branchings, on the con- 

 trary, are flat, jagged, and patulous at their extreme ter- 

 minations. 



The spined Spondyli, as the S. Gasdaropus, &c. are 

 mostly of one colour, as orange-red, purple, white, brown, 

 or yellow; which colours, in fine specimens, are exceeding- 

 ly brilliant. 



Those which have branches or plaits, (as the S. phcatus 

 &c.) have, on the contrary, aground colour of either of the 



