COycm UA.—niTHYRA. 23. ■ 



Mactra testd trigonti diaphand convexu suhcequilaterali, late- fiiprfa- 

 ribiis trimcatis, umbonibus prominu'is incurvis. 



Shell triangular transparent convex and nearly equilateral, trun- 

 cate at the sides, witb the beaks prominent and incurved. 



Alactra cinerea. Montagu, Test. Brit. Suppl. p. 35. 

 Pennant, Brit. Zool. iv. p. 196. 



Found at Weymouth, by Breyer. 



Montagu is of decided opinion that this is a very distinct species, 

 presenting the same difference from the Mactra Stultorum as 

 there is between the Mactra solida and Mactra truncata, with 

 respect to tiie depth of the shell, prominence of the bealis, and 

 flatness of the truncated sides. 



The valves of this Mactra, he observes, are more concave 

 than of the Mactra Stultorum, more angulated, and rather 

 broader in proportion to their length ; the beak slightly turued 

 to one side, beneath whicii is a depression or subarcuation in its 

 contour, on the opposite side much compressed laterally : it is 

 nearly destitute of markings, there being only one or two obso- 

 lete pale rays, and the margin only covered with an epidermis, 

 which is brown inclining to ferruginous at one end : inside pale 

 with a tinge of blush. 



Specimens answering to this distinction are not unfrequently 

 cast on the Paington sands, after an eastern gale. 



Mactra testd ovatu planiuseuld inaequilaterali transversim ciauc*. 



striatd, umbonibus incurvis. 

 Shell oval flattish inequilateral and striate transversely, with the 



beaks incurved. 



