388 SHELLS AND SHELL-FISH. PART II. 



Lima Linn. Longitudinally oval ; valves gaping on 

 one side near the umbones; animal similar to avicula, 

 connecting this family with the last. 



L. squamosa. Sow. Man. 174. 



Pecten Brug. Shell generally free, sometimes slightly 

 attached by a byssus ; orbicular or ovate ; auricles 

 nearly equal ; umbones central ; valves closing all 

 round ; hinge margin straight ; no teeth ; ligament 

 triangular, internal. 



Decadopecten Riippell. General form of Pecten, but 

 with plicated teeth of the hinge : analogous to Nucula. 

 D. plicata Sow. Man. f. 172. 



Pleuronectia Sw. General form of Pecten, but the 

 valves very much compressed and gaping at their 

 edges. 



P. laevigata Sw. En. Meth. 208. f. 3. 



Hinnites Def. Animal attached ; shell pectiniform, but 

 irregular. 



H. pusio. Sow. Man. f. 173. 



Spondylus. Shell inequivalve, attached by its under 

 valve ; rough, with spines and plates ; umbones 

 central, remote, separated by a triangular disk. 



Plagiostoma ^ow. Shell free, inequilateral, oblique; um- 

 bones remote ; sub-auriculated on one side ; hinge 

 straight in one valve, with a triangular notch in the 

 other ; surface spinous or smooth. Fossil only. 

 P. spinosum. Sow. Man. f. 176. 



Spondylus Lam. Shell attached ; spinous and foliaceous 

 externally; auriculated hinge, with two teeth locking 

 into cavities (Jig. 129. a.) 



S. Americanus. Sow. Man. f. 177. 



Dianchora Sow. Shell attached, obliquely pectiniform, 

 the attached valve having an opening at the boss, 

 the other auriculated with an obtuse boss ; teeth 

 none ; passing into Ostrea by Pedum. 

 D. striata. Sow. Man. f. 175. 



