CONCRYUk—DITHYRA. 1. 



frontal gape, the smaller end is rounded, and not as in the laif 

 species truncate, and it has no accessorial valves. In adclitidh; 

 also, to the other marks of discrimination, it maybe observed, 

 that the valves of the Pholas papyracea are closed in front by a 

 fine elastic membrane, in the middle of which, near the base or 

 rounded extremity, is a small orifice or spiracle, which can be 

 closed at pleasure^, and through which water is often ejected. 



Mrs. Griffiths, who has herself taken them from their native 

 rocks, and given much attention to the subject; observes that the 

 animals are quite different. 



Pholas testd latere antico hiante, margine supra denies tuber- tubereuiata 



eulo scabrOf accessorio unico cardinali. 

 Shell open at the anterior end, with a rough tubercle on the 



margin above the teeth, and a single accessorial valve at the 



hinge. 



Tab. nost. 1, fig. 7 and 8. 

 3Jus. nost. Found with the last, thongh very rarely. 



Shell three quarters of an inch long, and an inch and a half 

 broad, oval, white, with a single oblong accessorial valve at the 

 back, which reaches to the anterior tertnination, where the valves 

 meet together and are scarcely elongated ' into a beak; the 

 opening or gape nearly orbicular. 



The surface of the anterior end'fs covered with close-set 

 oblique transverse rough ribs, which are straighter beyond the 

 longitudinal groove, and gradually disappear towards the smaller 

 end which is rounded and nearly closed : inside with a longitu- 



