28 



This species belongs to the flat group which on this continent is typi- 

 fied by S, perplana, Conrad. It differs from all the ordinary forms of 

 that group by its greater size and coarser radiating strise. It resembles 

 >S^. magnifica, Hall, and occurs in nearly the same geological horizon. It 

 is, however, a good deal more flattened about the umbo of the ventral 

 valve, and has much smaller muscular scars. In S. magnifica the scars 

 are generally three-fifths the length of the shell ; in S. Irene they are 

 only a little more than two-fifths. The radiating stria? of ;S'. Irene are of 

 a very uniform size, as exhibited in about thirty individuals examined, 

 always four or five in two lines, but, according to the figures given in the 

 Pal., N. Y., vol. Ill, those of S. magnifica vary from three to ten or. twelve 

 in the same width : and, besides, the grooves between them are repre- 

 sented as distinctly punctate. 



Locality and Formation. — Grand Greve, Gasp^ Bay, No. 8. 



Collectors.— '^\\: W. E. Logan, R. Bell. 



Strophomena Blainvillei. (N. sp.) 



Plate 2, figs. 1, la, lb. PI. 3, fig. 1. 



Description, — Shell semi-elliptical, hinge line equal to a little less or a 

 little greater than the width ; sides in the posterior half usually gently 

 concave, sometimes straight or gently convex ; front broadly rounded, 

 sometimes straitish in the middle; width from one-eighth to one-sixth 

 greater than the length. 



Ventral valve gently convex ; greatest elevation about one-third the 

 length from the beak ; cardinal angles compressed ; the umbo broadly 

 obtuse ; beak scarcely distinct from the cardinal edge ; area flat, inclined 

 at an angle of about 40^ to the plane of the lateral margin, striated and 

 with the edge denticulated its whole length ; dorsal valve nearly flat, 

 slightly concave ; area very narrow ; both valves usually with several 

 concentric wrinkles or rugae of growth. 



Surface covered with fine, rounded or sub-angular radiating striae, of a 

 very uniform size; about twelve in the width of two lines. When slightly 

 exfoliated the grooves between the elevated stri^ are seen to be regularly 

 pitted or punctated, from six to eight punctures in one line. 



In the interior of the ventral valve the area occupied by the muscular 

 impressions is of a sub-triangular shape, and extends from the beak about 

 two-thirds of the length. The front of this area is generally broadly 

 rounded ; the two upper sides converging with a concave curve to the 

 beak. The space on each side of the upper part of the area is strongly 

 tuberculated, becoming gradually smooth towards the cardinal angles. A 



