LIMA. 269 



although the last described of our British Limce, was known 

 to the student of general Conchology, long before the 

 days of Montagu (who first introduced a member of this 

 genus into the Fauna of Great Britain), readily enables us 

 to discriminate specimens, however aberrant, from the two 

 other species which inhabit our islands. The form is 

 obliquely and unsymmetrically suboval, and more produced 

 than in most species of its genus. It is much and rather 

 suddenly attenuated above, narrowed and moderately 

 arcuated below, and decidedly gaping at both extremities. 

 The front hiation is extremely large, forms a narrow oval 

 cavity as far as the bend of the anterior side, and then 

 rather abruptly contracting, extends with very gradual di- 

 minution even to the ventral margin. The hinder gape is 

 much narrower, and in the young shell, where it is almost 

 linear, is only manifested on the lower portion of the 

 valves, but in the adult (where the valves only touch at 

 the hinge-margin and its opposite edge) is continued up- 

 ward, attenuating as it proceeds, even to the auricles. At 

 this stage, then, the hiation is conversely dilated on the two 

 sides. The snow-white valves, which are very inequilateral, 

 are apt to become stained with brown in the larger indi- 

 viduals ; they are, when adult, less translucent than in 

 Loscombii, and although thin and fragile, yet comparatively 

 firm in texture. They are chiefly ventricose, if at all so, 

 at the umbonal region, but when separated are decidedly 

 shallow. The exterior is almost entirely covered with very 

 numerous close-set costellar striae, which are more or less 

 roughened, and somewhat squamosely so, by concentric lines 

 of increase ; occasionally a raised interstitial stria likewise 

 presents itself between each of the larger ones. The 

 anterior side of the shell at first slopes forward, and 

 generally with but little convexity ; after proceeding about 



