12 CONCHY UX—DITHYR A. I. 



very wide, and reacliing nearly to the smaller end vvhicli termi- 

 nates in a rounded point, sloping suddenly at the anterior end 

 into a short rounded beak, giving that part an angular appear- 

 ance: the anterior part furnished with regular echinated stria? 

 separated by a fine depressed line from the smaller part, which is 

 marked with smooth and rather distant strise: the hinge at the 

 back covered with a long flat process, reflecting backwards, and 

 nearly in contact with the back in each valve: on tlie inner or 

 concave surface of the valves is a short rounded longitudinal rib, 

 crossed by rough points, growing stronger as it reaches the outer 

 margin: this interior rib, which is always visible in consequence 

 of the very wide gape, will at all times distinguish the species. 



The accessorial valves are five in number : two shield-like ones 

 in front, which nearly dose up the vast gape, and a narrow one 

 down the middle; a heart-shaped one behind covering the hinge 

 and a narrow one beneath it which connects the valves. 



It is probable that the presence or absence of the two shield- 

 like valves in front, occasioned Linne to form trvo species, and to 

 cause such uncertainty of identity among subsequent authors. 



Mrs. Griffiths has procured a dead specimen of the Pholas 

 crispata from the rocks in the neighbourhood of Torquay, and 

 ourselves liave taken the seven others; so that the whole of the 

 eight British species have been found in the highly productive 

 sliores of Torbay. 



