86 PALEONTOLOGY OF OHIO. 



MODIOLOPSIS TRUNCATUS. 



Plate 2, fig. 13. 



Modiolopsis Iruncatus, Hall ; Pal. N. Y., Vol. I., p. 296, pi. 81, fig. 3. 



Comp. Anodontopsis unionoides, Meek ; Pal. Ohio, Vol. 1., p. 141, pi. 12, fig. 2. 



Shell below the medium size ; shortly ovate in outline, the widest part 

 being about one-third of the entire length from the posterior end. Valves 

 compressed, or depressed convex, most prominent near the center. 

 Beaks small and closely comi")ressed, scarcely projecting beyond the line 

 of the hinge. Anterior margin rather shortly rounded, the extremity 

 extending but little beyond the beaks; basal margin gently and regu- 

 larly curving ; posterior end more broadly rounded than the anterior, 

 and most abruptly at the postero-basal portion; above, it slopes more 

 gradually backwards to the extremity of the hinge line, with which it 

 unites without forming any perceptible angle. 



Surface of the valves marked by irregular, rather strong, concentric 

 lines of growth. 



The internal casts — the condition in which the species is usually found 

 in the softer parts of the formation — show a large, elongate posterior 

 muscular scar, situated a little within the postero-cardinal margin, and 

 parallel with it ; also a smaller lunate anterior scar, and an entire pallial 

 line. The hinge plate would seem to have been of considerable width, 

 but its features have not been observed in specimens from Ohio. Those 

 from the sandy shales of the formation in New York show it to have been 

 a true Modiolopsis. 



Formation mid locality: The species appears to have been not uncommon in the 

 soft shales of the Hudson River group, in the vicinity of Cincinnati, Ohio, as speci- 

 mens have been derived from several sources with this label. Examples have also 

 been received from Prof. Edward Orton, from the more compact layers at the base of 

 the formation, at Frankfort, Kentucky. We are also strongly inclined to believe that 

 the specimen figured in Vol. I., Pal. Ohio, pi. 12, fig. 2, under the name Anodontopsis 

 unionoides, will prove to belong to this species. 



Modiolopsis concentrica (n. sp.). 



Plate 2, fig. 18. ' 

 Shell of medium size; elongate ovate in outline; broadest near the 

 posterior end, and contracted in front of the beaks. Hinge line arcuate, 

 gradually declining toward the extremity and rounding into the poste- 

 rior margin, which is more sharply rounded below than above the mid- 



