426 MACTRID^E. 



curved on the anterior side and nearly straight on the other 

 side : beaks sharp, triangular, and incurved, turned towards 

 the anterior side ; umhones swollen, prominent and project- 

 ing : ligament short and comparatively slight, reddish-brown : 

 cartilage large, but not otherwise different from that of its 

 congeners : hinge-line curved : hinge-plate extremely broad, 

 reflected over the dorsal margins, strong, not flexuous because 

 the cartilage-pit is scarcely advanced beyond the inner edge of 

 the plate : teeth, in the right valve two short erect cardinals, 

 united behind and diverging from each other at a right angle ; 

 laterals two on each side, and of the same description as in 

 M. stultorum ; in the left valve two united cardinals, and a 

 single lateral on each side similar to those in the last species, 

 except as to size and in the laterals rising from the beak to a 

 rounded point at each end and then abruptly falling and con- 

 tinued towards the front in a ridge -like form : inside coloured 

 like the outside and showing the rays, slightly and irregularly 

 striated in a longitudinal direction : paUial scar as in the last 

 species : muscular scars triangularly oval, well marked. L. 3. 

 B.4. 



Var. luteola. Shell creamcolour, without rays but stained 

 with reddish-brown or chestnut on the dorsal margins. 



HABITAT : Confined to a very few parts of our south- 

 ern shores, viz. Hayle, Cornwall, where single valves 

 were first found by Miss Pocock, subsequently by 

 Lieut. -General Bingham, and since by Mr. Templer, 

 Mr. Jordan, and Mr. Hockin ; Herm and Guernsey, at 

 unusually low tides (Lukis) . The variety is from Hayle. 

 Fossil in the Red Crag (S.Wood); Tarenti (Philippi). 

 The foreign localities are the north of France; Spain 

 and Portugal (Chemnitz) ; Gulf of Lyons (Martin) ; and 

 the Mediterranean, including Algiers (Poupillet). 



A series of this handsome shell was presented to me 

 by the late Dr. Lukis, who afterwards sent me an ex- 

 quisite drawing of the animal, which has enabled me to 

 give a description of that part. He observed that " when 

 the tide recedes it buries itself two or three inches in 

 the sand ; and when the tide rises it bestirs itself like 



