CO^CHYUX—DITHTRA. 6. 25 



HiATELLA testa latere postico rotundato areold nulla, antico obionga. 



subangulato hiante. 

 Shell rounded at the hinder end without impression, truncate and 



somewhat angular at the anterior. 



Tah. nost. 2, fig. 1.3. 

 Mus. nost. Frdm rocks in Dublin bay and Torbay. 



Shell three-eighths of an inch long, and about an inch broad, 

 oblong, whitish, transversely striate, rounded at one end, some- 

 what truncate and much open at the other ; the valves rather 

 unequal, with an obscure, oblique, and nearly smooth angle from 

 the beaks to the anterior end : beaks prominent : teeth as in the 

 last. 



The specimens which we have collected, both in Ireland and 

 Torbay, preserve the regular distinction of having the hinder 

 extremity well rounded and without impression, and the anterior 

 much gaping, with the beaks not terminal, and the transverse 

 angles rather obscure, and generally smooth. 



6. PETmCOhk—LAMAMCK. 



Testa subtransversa, eequivalvis, itKpquilateralis, latere antico 

 hiante. Cardo dentibus duobus inter tres peneirantibus : 

 tateralibus nullis. Ligamentum externum. 



E 



