Contributions to Invertebrate Palseontology. 54T 



L.ingula ligea ? 



Plate XI, figs. 3 and 4. 

 ? Lingula ligea Hall ; Pal. N. Y., vol. 4, part 1, p. 7, pi. 1, fig. 2. 



Shell elongate elliptical in general outline, being about twice as long as 

 ■wide, rounded on the anterior end, and slightly more pointed at the beak in 

 full grown forms ; but in young or partly grown shells the extremities appear 

 nearly equal. Valves moderately convex, and sometimes a very little flattened 

 along the middle. Surface marked by fine concentric lines of growth. 



The examples referred with some slight doubt to this species are 

 quite numerous in the thin bedded layers of bituminous limestones 

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

 Columbus, Ohio. The young shells have much the appearance of 

 L. spatulata Hall, but when fully grown are almost exactly of the 

 character of L. ligera. 



Genus DISCIIVA Lamarck. 



Discina minuta. 



Plate XI, figs. 5 and 6. 

 Orhicula minuta Hall, Geol. Kept. 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 

 occui-ring 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. Sur- 

 face 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 shales capping the 

 Upper Helderberg limestone near Dublin, Ohio. 



Discina L.odensis. 



Plate XI, fig. 7. 

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

 Orhicula Lodensis Vanuxem, Geol. Rept. 3d Dist. N. Y., p. 168. 

 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. 2,'i-29. 



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

 the black shales. The form is subcircular and discoid, a little nar- 



