140 Cincinnati Society of Nutiiral History. 



becoming nearly vertical along the nmboes. Body of the valve broadl}' 

 sinuate between the anterior and posterior umboual ndges, and tlie 

 anterior end abruptly stopping. 



Surfoce of the shell marked by numerous, distinct, concentric undu- 

 lations, with the appearance of fine, radiating lines, which seem to haA'e 

 formed elongated pustules along the posterior umbonal ridge in the 

 more advanced stages of growth. 



This species is a very marked one in its general form and rhom- 

 boidal outline, as well as in the general expression of the surface. It 

 IS closely related to Orthodesma contracta, Hall sp., from this same 

 horizon, but may be readily distinguished by the shorter anterior end, 

 more angular beaks, and by the longest point of the anterior extremit}' 

 being situated near the cardinal line, instead of below the middle of 

 the shell, as in that species. 



Formation and localit}^: In the Hudson River Group, at Cincinnati, 

 Ohio. The specimen was found near the top of the hills back of the 

 city, about 360 feet above low water mark of the Ohio river. 



Sedgevtickia (?) LUNULATA, u. sp. (Plate VI., figs. 8, 8a.) 



Shell small, irregularly sub-ovate in outline, and quite veutricose; 

 with large, tumid, sub-central beaks: length equal to about once and a 

 half the height. The hinge line on what we have considered the posterior 

 side, is straight, and almost half as long as the entire length of the 

 sh6ll, but without any appearance of an escutcheon, and showing, to a 

 slight degree, evidence of an external ligament, extending nearly its 

 entire length. On the opposite (anterior) side of the beaks, the cardi- 

 nal line slopes rapidly toward the base, contracting the height of this 

 side to about half that at the beaks, and is deeply excavated, forming 

 a very large and deep lunular cavit3^ below which the extremity- is 

 narrowly rounded to the basal line. Base nearly straight along the 

 middle and for half the length of the shell, and rounding abruptlj' to the 

 hinge on the larger (posterior) end. 



Surface of the shell marked by rather large, concentric undulations, 

 which become strongly developed as they approach the margins of the 

 lunule; and also by finer intermediate lines of growth. 



This species is undoubtedly congeneric with those forms described 

 by Prof. Meek, from these same rocks, and referred with doubt to 

 the genus Sedgewickia, McCo}', but we do not think them generical 

 with the typical forms of that genus as illustrated b}' its author, tak- 

 ing the earliest species given; but as we know of no established genus 

 to which they are more nearly related, and as they are not sufficiently 

 well defined to afford a clear generic diagnosis, we prefer to place this 

 one under the same generic designation, provisionally, i-ather than 



