CO'^CEYLIA—DITHYRA. 1. | 



frontal gape, the smaller end is rounded, and not as in the last spe- 

 cies truncate, and it has no accessorial valves. In addition, also, 

 to the other marks of discrimination, it may be 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 ex- 

 tremity, is a small orifice or spiracle, which can be closed at plea- 

 sure, 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 testa latere antico hiante, margine supra denies tuberculo Tuberculata 



scahro, 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. 

 Mus. nost. Found with the last, though 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 termination, where the valves 

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

 or gape nearly orbicular. 



The surface of the anterior end is 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- 



