212 
Kirtley F. Mather 
Nucula sp. 
Description. Shell small, sub-triangular in outline, convexity 
low; anterio-dorsal margin nearly straight, meeting the ventral 
margin in an acute angle ; posterio-dorsal margin slightly convex 
and much shorter than anterio-dorsal; ventral margin convex, 
curving abruptly into the anterio-dorsal and more gently into the 
posterio-dorsal margin ; beak not tumid and only slightly elevated 
above the hinge-line, situated behind the middle and directed 
posteriorly ; taxodont dentition indicated by impressions of teeth 
along hinge-line; surface of cast smooth. 
Remarks. The cast of a left valve of a Nucula upon which 
this description is based bears strong resemblance to N. illinois- 
ensis Worthen and to N. montpelierensis Girty but its characters 
are not sufficiently defined to permit of accurate specific deter- 
mination. 
Horizon and locality. Kessler limestone : East Mountain, Fay- 
etteville, Arkansas (Station 209). 
LEDID^ 
Genus LEDA Schumacher 
Leda bellistriata Stevens ? 
Plate XV, figure 19. 
1858. Leda bellistriata. Stevens, Am. Jour. Sci., 2nd ser., vol. 25, p. 261. 
Coal Measures: Danville, Illinois; Summit, Ohio. 
1858. Nucula (Leda) Kazanensis. Swallow, Trans. St. Louis Acad. Sci., 
vol. 1, p. 190. (Not N. kazanensis Verneuil, 1845.) 
Upper and Lower Permian: Valley of Cottonwood and near Smoky 
Hill Fork, Kansas. 
1858. Leda bellistriata. Hall, Geol. Iowa, vol. 1, pt. 2, p. 717, pi. 29, 
figs. Ga-d. 
Lower Coal Measures: Illinois. 
1862. Leda bellistriata. iWinchell, Proc. Acad. Nat. Sci., Phil., p. 419. 
Marshall Group: Moscow, Michigan. 
18’65. Leda bellistriata. 'Winchell, Proc. Acad. Nat, Sci., Phil., p. 128. 
Marshall Group: Hillsdale, Michigan. 
1869. Leda bellistriata ?. Winchell, Safford’s Geol. Tenn., p. 444. 
Shales just above Black shale: Hickman and Maury Counties, 
Tennessee. 
1870. Leda bellistriata ?. Winchell, Proc. Am. Phil. Soc., vol. 11, p. 256. 
Waverly Group: Tennessee. 
