Silurian Fossils of Canada, 53 



Strophomena nitens. N. s. 



Fig. 1. — Strophomena nitens. a is a section shewing the curvature and 

 obtuse angles formed by the inclination of the areas. 



Description. — Transversely semi-oval, sides somewhat straight 

 for one third or a little more of the length from the cardinal 

 angles, and slightly converging towards each other; front angles 

 broadly rounded; front margin gently convex or nearly straight 

 for about one third the width in the middle portion. Wid h on 

 hinge-line from nine to twelve lines. Length from six to eight 

 lines. 



The beak, umbo, depressions on each side of the umbo and 

 the cardinal angles of the ventral valve the same as in S. al- 

 ternata. The deflected margin forms an angle of between 100^ 

 and 110^ with the general plane of the visceral disc, and occu- 

 pies on the median line (in all the specimens I have seen) from 

 one third to nearly one half the whole length of the shell. 



The dorsal valve is quite flat, or even a little concave, just in 

 front of the beak, but elsewhere curved to correspond with the 

 ventral valve. 



The area of the ventral valve lies nearly in the plane of the 

 lateral margin^, and the area of the dorsal valve forms with it an 

 angle of about 95^. The height of the area of the ventral valve 

 at the foramen is three fourths of a hne in a specimen nine lines 

 wide, and of the dorsal valve about one third of a line. Foramen 

 of ventral valve partly closed by a V-shaped deltidium, the lower 

 open part of which is closed by the strongly projecting deltidium 

 of the dorsal valve. 



The width of the foramen is about equal to its height. 



The surface is the same as in S. alternata, and, when a little 

 worn, presents a smooth shining silken lustre. 



When compared with S. incrassata, S' alternata, S. deltoidea , 

 S. camerata, or *S^. teniiistriata^ it will be seen that this species is 

 shorter in proportion to the width than any of theni, and also 

 that the inclination of the areas towards each other differs in 

 forming an obtuse instead of an acute angle. 



