10 Cincinnati Society of Natural History. 



others, the interior is smooth. Ventral margin of the right valve over- 

 lapping that of the left, and on the interior thickened and grooved, t«» 

 admit the ventral edge of the left valve. Substance of the valves thin. 



The form of the valves and their radially striate surface, will serve 

 to readily distinguish the species from any other species of the genus 

 known to the writer. 



Formation and locality- : The specimens were found in the Utica 

 shale, exposed below the banks of the Ohio River, in the First Ward of 

 Cincinnati. 



Collectors : J. Fine, H. E. Dickhaut, E. O. Ulrich. 



Leperditia crepiformis, n sp. (Plate VII., figs. 3, 3r/,) 



[Ety. — Crepis, a horse-shoe; formis, form.] 



Length, .02; breadth, .015 inch. 



Carapace minute, broadly elliptical or reniform; dorsal margin 

 .straight or slightly convex, with hinge line much shorter than the 

 entire length of the valve; anterior and posterior extremities sub- 

 equal, rounded, the former end being sometimes slightly more obtuse 

 than the latter; ventral margin uniformly rounded. Valves moderate 

 ly convex. Tubercle or ridge arising abruptly, very prominent, and 

 shaped like a horse-shoe, placed on the anterior half of the valve: the 

 two sides of the " horse shoe"' are rectangular to the dorsal margin, and 

 extend from the same across the valve to the ventral margin; the an- 

 terior half of the ridge arises immediately from the anterior extremity ; 

 width of the ridge equal to about one fourth of the width of the valve; 

 a deep sulcus, between the anterior and posterior halves of the ridge, 

 extends from the dorsal margin to three fourths the distance across 

 the valve. Surface smooth. Interior marked by a horseshoe shaped 

 depression corresponding to the ridge of that form on the exterior. 



This species is too distinct to necessitate a comparison with other 

 species of the genus. 



Formation and locality: in the lower part of the Hudson River 

 Group, at Covington, Ky. 



Collector: E. O. Ulrich. 



Leperditia unicornis, n. sp. (Plate VII., figs. 4, 4r/, 46.) 



[^ly . — Unicornis , one-horned.] 



Length, .035; breadth, .02 inch. 



Carapace minute, sub quadrate, or obtusely elliptical, rather narrow; 

 anterior and posterior ends nearly equal, broadly rounded , valves very 

 convex, with abruptly sloping margins, and cylindrical ; dorsal edge 



