NATURAL SCIENCES OF PHILADELPHIA. G5 



CONOCARDIUM OHIOENSE, Meek. 



Shell rather small, longitudinally subovate or sulitrigonal, 

 being widest and most convex anteriorly ,i where the valves are 

 rather distinctly ventricose ; posterior side produced and abruptly 

 contracted behind the gibbous anterior region, partl}^ from lateral 

 compression, and partly from the upward and backward slope of 

 the posterior basal margin, which is slightly sinuous near tlie ex- 

 tremity, and distinctly gaping, the widest part of the hiatus being 

 above ; hinge-line straight, or sometimes slightly declining at the 

 posterior extremity; cardinal margins of the valves aiichylosed; 

 anterior side short, though not properly truncated, abruptl^^ con- 

 tracted and a little impressed in front of the umbonal convexity, 

 and apparently provided with a slender projection above (this 

 part broken in the specimens) ; beaks projecting a little above the 

 cardinal margin, placed in advance of the middle and incurved; 

 umbonal slopes gibbous, broadly rounded, and, like the beaks, 

 slightly inclined backward. Surface (as seen in specimens ap- 

 parently a little exfoliated) ornamented by simple, somewhat 

 flattened, radiating costse, about five or six of which, on the gib- 

 bous part of each valve, are separated by flattened furrows 

 nearly or quite as wide as the costaj themselves ; while on the 

 posterior contracted portion, the costse are proportionally wider, 

 and separated bj'" merely sharply impressed hair-lines, excepting 

 near the posterior cardinal margin, where these im})ressed linear 

 furrows are represented by little raised lines ; costae on the ante- 

 rior surface more obscure ; fine regular lines, and a few stronger 

 marks of growth, are also seen crossing the costse parallel to the 

 free margins. 



Length of a specimen with the anterior attenuated appendage 

 broken away, 0.64 inch ; height, 0.43 inch ; convexity, 0.37 inch. 



This species belongs to the section of the genus that has the 

 umbonal slopes rounded instead of angular, and the anterior 

 side in front of these slopes not so distinctly truncated or flat- 

 tened as to impart the peculiar Hemicardium-like appearance so 

 often seen in the genus. These characters at once distinguish it 

 from its associate, G. trigonale, Hall, sp. ; which is also distin- 



' I merely follow the most general adopted method of describing the 

 gaping end as the posterior, without being entirely satisfied that this is the 

 correct view. 

 1871.] 



