26 



Cincinnati Society of Natural History. 



nearly flat, though slightly convex in the umbonal region ; 

 hinge line straight, longer than the body of the shell, though 

 not equal to the height ; anterior wing short, extending, 

 however, in the older shells somewhat acutely beyond the 

 margin of the shell ; posterior wing triangular, extending in 

 mature forms as far as the body of the shell, and terminating 

 in an acute point ; surface of the left valve marked by con- 

 centric striae that become more and more distant from each 

 other from the beak to the base. There are no longitudinal 

 radii or lines. Surface of the right valve smooth, except a 

 series of wrinkles on each wing are directed obliquely from 

 the cardinal line toward the body of the shell, but fade away 

 at the sulci. 



This species has been generally classed with Pterinea 

 insueta of the Utica Slate of New York, but the shells are 

 quite different in form, especially in the shape of the anterior 

 wing, and also in the surface ornamentation. There are 

 longitudinal radiating striae along the middle of Pteri?iea 

 insueta, none of which exist in this species, and the con- 

 centric markings on P. insueta consist of finer and coarser 

 striae and wrinkles, while on this species the concentric striae 

 are smooth, of uniform size, and become more and more 

 distant from each other as they approach the base of the 

 shell. Pterinea insueta is not known to occur in the rocks 

 in the vicinity of Cincinnati, and so far as we are informed, 

 it is confined to the Utica Slate of New York. 



This species is not rare in the middle part of the Hudson 

 River Group, especially at the stone quarries on the hills 

 about Cincinnati. The specimens illustrated are from the 

 collections belonging to the authors. 



Pterinea rugatula, n. sp. 



t 



Plate /, Fig. 18; view of the left valve of a large specimen, 

 having some of the margin broken away; Fig. 19, view of the 

 left valve of a smaller and more perfect specimen. 



Shell below medium size, oblique, subrhomboidal ; body, 

 without the wings, oblique-ovate, hinge line straight, about 



