342 PALEONTOLOGY OF OHIO. 



it differs so decidedly from the type of that species in form that I think 

 it can hardly belong to the same species. When the figure was prepared 

 I had intended to make thorough comparisons with A. vera, but circum- 

 stances beyond my control have prevented this. 



Locality and position : Same as last. 



Genus CTPRICARDmA, Hall, 1860. 



(Palseont. N. Y., III., 266.) 



Cypeicaedina ? CAEBONAEiA, Meek. 



Plate 19, figs. 8a, h. 

 Cypricdrdinaf carbonwria, Meek (1871) ; Proceed. Acad. Nat. Sci., Philad., XXIII., 163. 



Shell small, longitudinally oval, less than twice as long as high, the 

 widest (highest) part being under the posterior extremity of the hinge ; 

 rather gibbous, with usually a broad impression extending from the 

 beaks obliquely backward and downward to the middle of the base of 

 each valve; anterior side extremely short, or nearly obsolete, convex, 

 and rounded; posterior side broader, more compressed or cuneate, with 

 its upper edge straight and sloping obliquely backward to the regularly 

 rounded posterior margin ; base broadly and slightly sinuous in the mid- 

 dle, and rounding upward at the extremities; hinge line straight, be- 

 tween one-half and two-thirds as long as the valves, ranging at an angle 

 of about 25° with the oblique, longer axis of the shell, so as to meet the 

 sloping upper edge of the posterior margin at a very obtuse but mod- 

 erately well-defined angle, thus imparting to the somewhat compressed 

 posterior dorsal region a very faintly alate appearance ; beaks extremely 

 oblique, depressed nearly to the dorsal margin, very nearly terminal, and 

 scarcely projecting beyond the rounded outline of the anterior extrem- 

 ity. Surface ornamented by about fifteen to twenty exceedingly regular, 

 well-defined, subimbricating, flattened, concentric ridges or undulations, 

 that gradually become smaller and more closely approximating on the 

 umbones. 



Length of largest specimen seen, 0.55 inch; height at the posterior 

 extremity of the hinge, 0.32 inch; convexity about 0.18 inch; length of 

 hinge, about 0.30 inch. 



This little shell has nearly exactly all the external characters of Cypri- 

 cardina (C. lamellosa, Hall), as found in the Upper Silurian, excepting 

 that its beaks are more nearly terminal, and its concentric markings or 



