88 PALEONTOLOGY OF OHIO. 



MODIOLOPSIS CiNCINNATIENSIS (ll. Sp.)- 



Plate 2, figs. 14, 15. 



Shell of medium size or smaller ; elongate ovate, or narrowly sub-ellip- 

 tical in outline ; widest posteriorly, and abruptly contracted in front of 

 the beaks ; hinge line slightly arcuate, and a little more than half as 

 long as the' shell posterior to the beaks ; posterior margin obliquely slop- 

 ing, with a slight convexity, from the extremity of the hinge line to 

 the postero-basal angle, which is the point of greatest length of the shell. 

 Basal line gently curving throughout its length in most cases, but in 

 some examples becoming slightly sinuate opposite or a little posterior 

 to the beaks. Anterior end narrow, not very extended, and sharply 

 rounded. Beaks small, appressed; projecting but little above the hinge 

 line, and situated just within the anterior third of the length of the 

 shell. General surface of the shell moderately convex ; most prominent 

 along the posterior umbonal ridge, which is sharply rounded or obscurely 

 angular ; umbonal slope abrupt and slightly convex. An obscure, shal- 

 low mesial depression extends across the valves from the beaks, reach- 

 ing the basal line just behind the anterior third of the length. 



Surface marked by numerous, irregular, concentric lines of growth, 

 which are often strongly marked, but without any definite arrangement ■ 

 a little stronger on the anterior portion of the shell than elsewhere- 

 The substance of the shell is thin, and the surface, when perfect, quite 

 polished. 



This species bears considerable resemblance to the larger specimens of 

 the form identified with and figured as M. anodontoides, Conr., in Palaeon- 

 tology of New York, Vol. I, p. 298, pi. 82, fig. 36, but differs in the greater 

 breadth posteriorly, and in being much more contracted in width in front 

 of the beaks. From the other forms given on the same plate as the same 

 species it differs more strongly, and can not be readily confounded with 

 them. The specimen represented by fig. 3a of the same plate, which is 

 the original of the species used by Mr. Conrad for description, and that 

 which must be considered as possessing the true specific characters, is 

 much more angular along the umbonal ridge ; the hinge line is propor- 

 tionally longer, and the anterior end of the shell shorter and broader 

 than iu the species under consideration. 



Formation and locality : In limestone of the Hudson River group, near the base of 

 the formation, at Cincinnati, Ohio. 



