LEPTON. 203 



the dorsal margin, placed considerably nearer to the posterior 

 or narrower side, which is not half the size or breadth of the 

 anterior side : hinge-line obtusely triangular, occupying about 

 one-third of the circumference : cartilage rather large, situate 

 close to the beaks on the narrower side: hinge-plate rather 

 narrow but thick, deeply excavated in the middle : teeth, in the 

 left valve a strong and oblique cardinal, and a long laminar 

 pointed lateral on each side of the beak ; in the right valve a 

 very minute cardinal, with strong lateral teeth as in the other 

 valve ; all the laterals are nearly of equal size, and diverge a 

 little inwards from the hinge-line : inside nacreous and 

 glossy, with a plain margin : scars not very distinct. L. 0-085. 

 B. 0-1. 



HABITAT : Gravelly sand, at depths of from 18 to 80 

 fathoms, on various parts of our coast, but not every- 

 where. The localities being few, I will enumerate 

 them. Shetland, Arran Isle, co. Galway, Fowey (Bar- 

 lee) ; Exmouth (Clark) ; Plymouth (Rouse) ; Skye, Bar- 

 mouth, Lulworth, Torbay, Guernsey (J. G. J.). Al- 

 though this appears at present to be rather a scarce 

 species, it is hoped that something will be sooner or 

 later known of its distribution in other parts of the 

 European seas, as well as of the animal. The proba- 

 bilities are much against any of the marine inverte- 

 brata being exclusively confined to the line of soundings 

 round our own sea-girt coasts. 



The shell differs from that of any of its congeners in 

 the obliquely rounded outline, and especially in the 

 sculpture, which consists of fine and irregular con- 

 centric striae, instead of pit-marks or regular transverse 

 and parallel ribs. It is also marked with longitudinally 

 radiating lines, and the beaks are much nearer one end. 

 The structure of the hinge agrees better with that of 

 L. sulcatulum. 



