56 GEOLOGICAL AND NATURAL HISTORY SURVEY OF CANADA. 



Strepula LUNATIFERA, N. Sp. 

 PL IX., figs. 14, and 14/>. 



Yalves slightly elongate oval in outline, the posterior half generally 

 a little the highest. Dorsal edge straight, one-fifth shorter than the 

 length of the valve. Ends equally convex, rounding gently into the 

 nearly straight-ventral edge. Border strongly depressed, widest at the 

 posterior end. Marginal ridge thin, abruptly elevated, running paral- 

 lel with the border and overhanging it. Within the marginal ridge 

 the surface is slightly depressed, with two nearly vertical thin ridges 

 in the anterior half and two curved ones in the posterior. The latter 

 unite at their ends and enclose a crescent-shaped concave space, the 

 outer curve of which is almost parallel with the curve of the postero- 

 ventral margin. These curved ridges often extend to and unite with 

 the marginal ridge, and sometimes the upper end of the inner of the 

 two anterior i-idges is swollen and forms a more ov less prominent 

 node. 



Dimensions of a large valve : greatest length, 1.55 mm. ; greatest 

 height, 0.8*7 mm.; greatest. thickness of single valve, 0.32 mm. The 

 Ohio specimens are usually a little smaller than this, their average 

 length and height being, respectively, 1.25 and 0.7 mm. 



This fine ^"species is represented by a single valve on a small slab 

 collected by Dr. E. W. Ells in 18*75 at Siony Mountain, and a number 

 of specimens picked from washings of shale of the upper beds of the 

 HudsonJEiver or Cincinnati group, at Oxford, Ohio. It is related to 

 S. quadrilirata, Hall and Whitfiield, but the two are not sufficiently 

 similar to make confusion between them at all likely. 



