740 DR. J. E. GRAY ON THE CALYPTR^ID.E. [Juiie 27, 



cavity in the shelly plate of Mitrella ; but the plate is attached by 

 each of its side edges. 



The more convex species might be confounded with Crepipatella; 

 but they are always known by the fold forming a subcentral ridge 

 on the lower surface of the plate, and ending in the small shallow 

 pit like the scar of a muscle. 



This group has been regarded as a subgenus of Crypta ; but it is 

 more allied to Mitrella. 



1. ErGuEA, Adams ; Chenu. 



Shell nearly flat ; apex posterior, marginal ; nucleus spiral ; whorls 

 rapidly enlarging. 



The shells when they live in cavities are concave externally, — and 

 when living on a rough surface, corrugated like other Calyptrceidce. 



Erg^a walshi. 



Crepidula walshi, Hermannsen. (^C. plana, Chemx, Man. f. 2364. 

 Var. distorted and rugose, C. plana, Adams & Reeve.) 

 Hab. Ceylon ; Bombay. 



2. Noicia. 



Shell subcircular or oblong, convex, spiral ; whorls one and a half 

 or two ; the apex subcentral, subposterior ; nucleus spiral ; cavity 

 concave, deeper under the apex ; internal ])lates concave, thin, with 

 the fold forming a narrow linear cavity open to the apex of the shell, 



NoiciA CHiNENSis, n. s. (in Cuming's Collection). 



Shell pale brown, smooth, or slightly concentrically striated. 

 Hab. China. 



Var. Shell very thin, convex ; the internal plate thin, with the 

 fold only slightly marked and solid. 



Tribe IV. Shell conical, spiral; spire of few rajndly enlarging 

 whorls ; cavity conical, with a well-developed oblique subspiral 

 lamina on one side, from the tip, which has the inner or pillar- 

 edge reflexed, forming a pit or solid rib. Mitrellina. 



1. Mitrella. 



Shell conical, like Poculina ; but the internal plate is oblique and 

 subspiral ; the reflexed part of the pillar-lip is closely a])plied to the 

 plate, and only forming a thickened edge to the plate, there being a 

 small impression like the scar of a muscle at the lower part of it. 



I. Mitrella chinensis. 



Shell white or rosy ; outer surface with minute tubular spines or 

 tubercles. 



Patella chinensis, Montagu. 

 Calypfraea chinensis, Lamk., &c. 

 Hab. Coasts of Europe. 



