44 KI VALVES srONDVLUs. 



C. Ovate, a little angular near the beaks. 

 ♦Literata (Camp letteredV.) Cruentata. 

 *Geograpliica. Lutescens. 



Rotundata. Sanguiiiolenta. 



*Decussata. Argcntea. 



Virgiiica. Donacina. 



Virginica. Afra. 



*Rlioniboides. ' Dealbata. 



Lithophaga. 



SPONDYLUS. — Thorny Oyster or Articiioke- 



HEAD. 



Avimal — a Tethys: Shell hard, solids with unequal valves; 

 one of the valves convex, the other rather flat • hinge 

 with two recurved teeth separated bi/ a small hollow. 



This genus, though containing 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 

 witji each other. However, the usual character of the 

 Spond}lus 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 rami- 

 hcations or branchings, on the contrary, are flat, jagged, 



