CRENELLA. 211 



middle, and the two short dorsal edges, after forming a 

 nearly similar angle, run with equal arcuation to the well- 

 rounded base, so that the shell appears almost sym- 

 metrically equilateral, and very like a minute and earless 

 Lima. Holding it, however, in the same position as the 

 Modioli, we should describe the hinder dorsal edge, as 

 short, straightish, greatly ascending, and merging without 

 marked angularity, into the posterior margin, which latter 

 arching out with a bold sweep, and almost symmetrically 

 rounding the hinder termination, passes without inter- 

 ruption into the anterior or front ventral margin. Although 

 single valves are found of larger dimensions, we have seen no 

 pairs which have been taken in Great Britain, that measure 

 more than a sixth of an inch in length and an eighth of an 

 inch in breadth. Nevertheless, if, as we surmise, for we can 

 perceive no variation of specific importance, the glandula of 

 Totten prove identical, it attains to at least half an inch 

 at Maine and elsewhere in the United States of North 

 America. The shape of full-sized individuals of this Trans- 

 atlantic variety is more rhomboidal and much broader, 

 with a distinct curved anterior edge, which forms more 

 than a right angle with the hinder dorsal margin. 



This is a northern species, first discovei'ed by Laskey, 

 and, until of late years, specimens were rare in cabinets ; 

 the active exertions of Mr, Jeffreys, Mr. M 'Andrew, and 

 Mr. Barlee, in little explored localities, have made it more 

 common. On the English coast it has been found very 

 rarely at Scarborough by Mr. Bean ; oif the shores of 

 Northumberland, where it has been found at Oullercoats 

 and Fern Island by Mr. Alder, by Mr. King in the cavity 

 of a small stone from deep water, and by Mr. Howse, 

 alive in seventeen fathoms. On the coast of Scotland it 

 occurs in numerous localities from Oban round to the 



