442 GEOLOGY OF OHIO. 



above the "Bone-bed," at Smith and Price's quarries, near Columbus, 

 Ohio. The young shells have much the appearance of L. spahdata Hall, 

 but when fully grown are almost exactly of the character of L. ligea. 



Genus DISCINA Lamarck. 

 Discina minuta. 



Plate VII, figs. 5 and 6. 

 .Orbicula minuta Hall, Geol. Rept. 4th Dist. N. Y., p. 180. 

 Discina minuta Hall, Pal. N. Y., vol. 4, p. 16, pi. 1, fig. 16. 



Shell minute, subcircular. Dorsal valve moderately convex or flattened as 

 occurring in the shales, the apex situated a little nearest the posterior margin, often 

 about one-third of the diameter from the border, pointed and directed toward the 

 posterior or peduncular margin. Ventral valve not observed. Surface of the shell 

 marked only by closely arranged, very fine concentric striae. 



The shells of this species usually occur of about three-sixteenths of 

 an inch in diameter, and are usually very much flattened by compression 

 in the shales. They closely resemble those from the black Marcellus 

 shales of New York, but lack that convexity and finely polished surface 

 usually present on the Avon specimens. 



Formation and Locality. — In the brown shale capping of the Upper 

 Helderberg limestone near Dublin, Ohio. 



D sci?ia Lodensis. 



Plate VII, fig. 7. 

 Orbicula Lodensis Hall, Geol. Rept. 4th Dist. N. Y, p. 223. 

 Orbicula Lodensis Vanuxem, Geol. Rept. 3d Dist. N. Y., p 163. 

 Discina Lodensis Hall, Pal. N. Y., vol. 4, p. 22, pi. 1, fig. 14. 

 Discina media Hall, Pal. N. Y., vol. 4, p. 20, pi. 2, figs. 25-29. 



A single lower valve, referable to this species, was obtained from the 

 black shales. The form is subcircular and discoid, a little narrowed 

 toward the peduncular margin, and broadest forward of the middle. 

 Foramen comparatively small, narrowly elliptical, not extending quite to 

 the margin, the inner end not reaching to the centre of the disk; the 

 point of origin on the valve being slightly eccentric. Surface marked 

 by fine, not closely arranged, elevated, concentric lines. 



The specimen described and figured very closely resembles the New 

 York species above cited; so nearly so in fact as to preclude the possi- 

 bilit3 T of detecting specific differences. The specimens from New York 

 differ greatly among themselves in the general form and outline of the 

 valves; so that on this character alone it would not be safe to rely; and 

 the general features of the shell, so far as can be determined from a single 

 valve, are not the same in both cases. 



Formation and Locali y. — In the brown shales at the top of the 

 Upper Helderberg limestone near Dublin, Ohio. 



