107 



CRENATULA. 



ostrea picta. — Gmelin. 



Sowerbys Genera, No. 8, plate 4. 



The Crenatulae constitute a very remarkable genus, 

 somewhat resembling the G. Mytilus, but by the great 

 similarity of the hinge approaching nearer to the G. Per- 

 na: there is however this peculiar distinction, that in the 

 Crenatula the hinge is composed of slightly concave cal- 

 lous crenulations, which receive the ligament, while in 

 the Pernait consists of parallel truncated linear teeth, (or 

 rather rib-like joints), corresponding and opposed to the 

 opposite ones, the ligament being inserted only in their 

 interstices. Shells of this genus are thin and extremely 

 delicate; of a foliated texture, resembling the Placunae, 

 Aviculae, &c. more or less irregularly formed; valves 

 flattened, foliaceous, no distinct opening for the byssus : 

 hinge linear, marginal, with concave callous crenula- 

 tions, in which the ligament is inserted. 



Crenatula avicularis Crenulata bicostalis 



modiolaris viridis 



nigrina mytiloides 



Crenatula phasianoptera. 



