"Shell small, sub triangular to subcircular in outline. The lower 

 side is longest and is rather strongly curved, especially at the ends; 

 the anterior side is somewhat shorter and is gently convex; the poster- 

 ior side is much the shorter and is nearly straight or slightly concave. 

 The inferior-posterior angle is rather narrowly, the inferior-anterior 

 angle rather broadly, rounded. In a genus in which so many of the 

 species are strongly convex the convexity of N. subrotundata is gen- 

 erally rather low, though it varies greatly in different specimens 

 (partly due to the degree of maturity), and may be rather high. The 

 chief flextures occur near the anterior and posterior margins along 

 lines that make with each other an angle rather less than a right 

 angle. The inflected parts are narrow and project but little. On 

 the posterior side a "lunule" may be outlined by a faint sulcus which, 

 if present, tends to produce a slight emargination in the outline. A 

 few specimens referred under this species have the "lunule" distinctly 

 defined in this way. The beaks are not very prominent. They are 

 rather attenuated and are conspicuously turned backward. 



The shell is for its size very thick and massive, and it is marked 

 superficially by rather coarse, strong and regular concentric striae." 



Remarks. This species of Nucula is very abundant in the 

 Sharon and less so in the Harrison ore, but as far as is known, it is 

 confined in its occurrence in this State to these two horizons. It has, 

 moreover, been found only at a single locality in each member, and 

 only in the form of internal casts. The Ohio form differs from those 

 of the Morrow formation of Arkansas in being on the average a little 

 more gibbous. In the Sharon ore this species of Nucula is associated 

 with N.lunulata Girty mss. as in the Morrow formation, and also 

 with N.elongata n.sp. 



Horizon and locality. Harrison ore: Jackson County (Locality 

 1), c. Sharon ore: Lick Run, Scioto County (Locality 2), a. 



Nucula lunulata Girty mss. 

 PL IV, Figs. 7, 8, 9. 



Description. Another species of Nucula from the Sharon ore 

 is the same as Girty's manuscript form from the Morrow formation 

 of Arkansas, the description of which is quoted below: 



"Shell small and conspicuously triangular in shape. The width 

 and height are about equal. The convexity is great and the umbones 

 are very prominent. The cardinal and posterior parts of the shell 

 are strongly inflected along lines that are straight or slightly concave, 

 and that make with one another an angle of considerably less than 90. 

 The inflected parts are so directed that they are concealed when the 

 shell is viewed from either side. The inferior outline is gently convex 

 and is directed to the two other sides in such a way that the height of 

 the shell is nearly equal to the width and the posterior outline is 

 distinctly shorter than the anterior outline. Owing to the high con- 

 vexity and strong inflection of the margins a broad flattened surface 



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