Descripfions o^ New Genera and Species of Fossils. 11 



straight, nearly as long as tlie entire valve ; tubercle near the anterior 

 extremity prominent, pointed, directed anteriorly, and in some speci- 

 mens to such an extent, as to project beyond the margin of the valve; 

 the posterior third is sometimes tumid, and in that case there is :i 

 broad, slightly defined depression or sulcus, about in the middle of the 

 valve. Surface smooth, or rainutel_y pitted. Color, black. Substance 

 of valves thick. There is an internal pit corresponding to theanterioi- 

 tubercle. 



Leperditia (Isochilina) cylindrica, Hall, bears some resemblance to 

 this species. It is, however, comparatively longer, more uniformly 

 convex, somewhat different in outline, and with the tubercle obsolete. 



Numerous valves of this species were found associated with Leper- 

 ilit.ia minutissima and cylindrica. Hall; L. hyrnesi, Miller; L. bivertex. 

 Ulrich; a.nd Leptobolus lepis, Hall, in slabs of crystalline limestone, oc- 

 curring within fifty feet of low water mark in the Ohio River, about 

 one half a mile west of Covington, Ky. 



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



■ Leperditia bivertex, n. sp. (Plate VII., figs. 5, hn.) 



[Ety.— -B*»«rfea;,with two peaks,] 



Length, .04; breadth, .03 inch. 



Carapace minute, sub-reuiform ; dorsal margin straight, over two 

 thirds as long as the entire length of the valve ; anterior and posterior 

 extremities equal in width ; venti'al curve nearl}^ uniform. Valves 

 strongly convex. Tubercle at the anterior end, near the dorsal margin, 

 large, rising abruptl}^ obtusely rounded, and slightl}^ directed posteri 

 orlv. Posterior tubercle situated near the dorsal margin, and about 

 half the length of the valve from the posterior extremit}-, less obtusely 

 rounded, and more prominent than the anterior tubercle. Between the 

 tubercles there is a deep sulcus, extending from the dorsal margin to 

 one half the distance across the A^alve, Surface smooth. On the inte- 

 rior there is a corresponding pit for each tubercle, and a divisional 

 ridge between them. 



The species can be readily distinguished from Leperditia byrnesi, 

 S. A. Miller, which it most resembles, by the form and relative posi- 

 tions of the tubercles. In that species the posterior tubercle is nearer 

 the posterior margin, is much more prominent and pointed, and ex- 

 tends considerably beyond the dorsal margin. That species is also 

 comparativeh' longer. 



Formation, locality and collectors : same as the last. 



