270 OSTREADiE. 



two-fifths of its course, it rather abruptly changes its di- 

 rection, and runs subparallel to, but rather more obliquely 

 than, the straightish edge of the posterior side. The front 

 margin, as far as the curvature, is margined internally by a 

 thickening of the substance of the shell. The hinge-margin 

 is extremely short, frequently indeed, not more than 

 equalling a fifth of the breadth of the valves ; the edge 

 declines on both sides, and occasionally slopes, in the adult, 

 so remarkably behind, as to render the posterior auricle 

 obscure, especially when contrasted with the well-defined 

 and very acutely-tipped anterior one. The ligamental 

 area is large, and, in the full-grown examples, profound ; 

 the beaks are very acute and inclined. 



This shell attains to far larger dimensions than either of 

 our other species of Lima, individuals that measure an inch 

 and three-quarters in breadth, and about one-third less in 

 length, being by no means of uncommon occurrence in 

 North Britain. The southern examples are far smaller ; 

 those which we have taken in Guernsey, as well as those 

 from which Turton (the first to introduce the species as a 

 native of our coast) derived his description, being scarcely 

 more than half that size. We doubt, however, if these 

 were adult, as they agree in hiation, etc. with the younger 

 individuals of the northern ocean. The want of inter- 

 mediate specimens, and the very great rarity of those from 

 the south preventing a comparison, have caused the larger 

 northern shell to be esteemed a different species. 



The colour of the animal is often very beautiful, varying 

 from pale crimson to intense vermilion ; the mantle lobes 

 are often tinted with orange. The tentacula are ranged 

 in three distinct series, all towards the inner or attached 

 edges of the mantle lobes : the innermost row (that nearest 

 the shell) is much the shortest, the outermost longest, and 



