572 



Tenuis M. with a comprefled, fub-triangular, equilateral, 



femi-pellucid, thin, white (hell, concentrically wrinkled : 

 uvibo fmall, central, much produced, and not turning 

 to either fide. 



Infide moderately fmooth and gloflfy, with a broad, 

 but nearly obfolete, conic cicatrix, running to a point 

 acrofs the middle of the (hell, towards the beak : hinge 

 furnilhed with a bifurcated tooth, and a narrow fovio la ; 

 and remote, lateral, laminated teeth, one on each fide in 

 one valve; in the other a plain fingle tooth, with a 

 correfponding cartilage cavity, but no lateral laviin^. 

 Length a quarter of an inch ; breadth rather more. 



Wefirft difcovered this fpecies at Southampton, where 

 it is not uncommon on the (hore to the weft of the town: 

 and have fince received it from Mr. Bryer oi Weymouth. 



The hinge is fomewhat fimilar to that of M. comprejfa. 



but the fovioia is not fo broad, and is at once diftinguilh- 



ed by the lateral teeth, which that fliell is deftitute of: 



it differs alfo in fliape, being much more angulatcd, and 



' produced at the beak, as well as the cicatricula. 



In comparing it with the young of MaElra folida and 

 Stultorum, it differs from them, not only in (hape, but 

 effentially in the central, or primary teeth, and in pof- 

 feffmg lateral ones only in one va*Ive, which both valves 

 of thole fliells are furniflied with. 



The 



