OF DENISON UNIVERSITY. 
47 
the concentric markings were much more prominent. A peculiar fea- 
ture is the existence of two rib-like costae, extending from the beak to 
the front margin of the valve, which costae pertain to the sub-epider- 
mal part of the shell rather than the surface. Our second specimen, 
as figured on Plate i, is nearly circular in outline and with very little 
evidence of radiating striae, while the concentric markings are very 
prominent. This form may be distinguished from S. planoconvexa by 
the great convexity of the dorsal valves, as well as its greater size and the 
prominence of the beak of the ventral valve. Length, 14 mm, 
breadth, 13 mm., convexity, 8 mm. 
Procluctiis Cora, Owen. 
(Plate II, Fig. 26 ) 
Productus cora, Owen, Geol. Rep. Iowa, etc. PI. V, Fig. i. 1852. 
- Pfvduchis semireticulatus,Yidi\\. Stansbury’s Rep. Salt L. 41 1. 1852. 
P?'-oductus Prattenianus, Norwood. Journ. Acad. Phila. iii, 17. 1854. 
Productus O’ qinco status^ Shumard. Geol. Rep. Missouri, 201. 1855. 
Productus cora, Marcou. Geol. N. A. PL VI. Fig. 4. 1858. 
? Productus IcEvicostus, WhitQ. Journ. Post. Soc. N. H., VII. t86o. 
Productus Flemmgii^ Geinitz. Garb. -format, u. Dyas in Nebras- 
ka, 52. 1866. » 
Productus CalhounianiLs , Geinitz (not Swallow) do. 1866. 
Productus Konnickeanus^ Geinitz, (not de Verneuil) i860.. 
Productus Prattenianiis^ Meek. U. S. Geol. Surv. Net. 1872. 
ProductiLS Pi'attenianus White. Rep. U. S. Surv. 100 Mer. 
1877. Also referred to in Ohio Geology as P. aequicostatus. 
' This is the most abundant species of productus in the Carbonif- 
erous of Licking county, making up almost the mass of the rock in 
many places, so that slabs may be secured whose entire surface is 
studded with the remains of this fossil.- Yet, from the fragile charac- 
ter of the shell, it is rarely found not destroyed or broken. I trans- 
cribe Shumard’s original description as a basis for the study of our 
forms. 
“Shell large, broad, hinge-line equal to the greatest width of the 
shell. Dorsal valve much elevated, arched, visceral portion slightly 
flattened on the middle, sides falling rather abruptly to the ears. Ears 
large, triangular, with three or four broad folds, which are not con- 
