108 



PERNA. 



ostrea ephippium. — Linn. 



Sowerbifs Genera, No. 8, plate 5, 



It appears extraordinary that Linnaeus should have 

 classed these shells with the G. Ostrea, as the hinge is 

 so peculiar to themselves, and the byssus by which the 

 animal affixes itself, renders their separation natural 

 and expedient. The G.Perna nearly resembles the 

 G. Crenatula, though very distinctly and in many re- 

 spects differently characterized: the shells are sube- 

 quivalve, flat, somewhat misshapen, of a lamellar struc- 

 ture, the margins frequently thin and foliaceous; a 

 linear marginal hinge composed of sulcated tranverse 

 parallel teeth, or joints, not alternating with the op- 

 posite ones, but opposed to them, in the interstices 

 of which the ligament is insinuated; the posterior sinus 

 a little gaping, and placed beneath the extremity of 

 the hinge, through which the byssus passes; apices 

 small, almost equal, and situated at one extremity of the 

 hinge: the substance of the shell although solid, is form- 

 ed of flaky portions, not adhering closely to each other, 

 and giving it a foliaceous appearance. 



