PRODUCTELLJB OF THE CORNIFEROUS LIMESTONE. 157 



One or two specimens of larger dimensions in the Hamilton group have a simi- 

 lar surface-marking, but a different form. 



Geological formations and localities. In the Comiferous limestone in Schoharie 

 county, and in the Hamilton groug at Moscow and Pavilion, New- York. 



Productella sliumardiana. 



PLATE XXin. 



Productus skumardianus : Hall, Geol. Report of Iowa, Vol. i, Part ii, pa. 499, pi. iii, f. 9, and pi. vii, f. 1. 

 Producliu tpinuHcostus [in part] : Hall, Tenth Report on the State Cabinet, p. 173. 1857. 

 Products concentricut : Hall, Tenth Report on the State Cabinet, p. 180.* Geological Report of Iowa 



Vol. i, part ii, p. 517. 

 Productut pyxidatvt [partim Tel totom] : Hall, Geological Report of Iowa, Vol. i, part ii, p. 498. 



Shell concavo-convex, subhemispherical, wider than long : hinge-line 

 nearly or quite equalling and sometimes greater than the width of the 

 shell below. 



Ventral valve very convex, gibbous in the middle and on the umbo, 

 which is abruptly narrowed towards the beak, and the apex incurved 

 over the hinge-line ; the sides abruptly depressed towards the cardinal 

 extremities, which are flattened and more or less auriculate. In one 

 specimen observed, the apex is minutely truncate, and there is a 

 barely perceptible line at the junction of the two valves, which indi- 

 cates an area. 



Dorsal valve concave, often corresponding essentially with the ventral 

 valve ; but sometimes nearly flat in the upper and central portions, and 

 abruptly deflected towards the margin. 



The surface of the ventral valve is marked by intermittent radiating 

 ridges, gradually rising from the surface and terminating below in 

 elongate spines ; while upon the upper part of the shell, about the 

 umbo, there are scarcely perceptible elevations of the surface above 

 the bases of the spines. There are sometimes one, two, or more spines 

 upon the ears, but this does not appear to be a constant character : 

 the entire surface is marked by close concentric undulating striae. 



• The Geological Report of Progress referred to in this and one or two other instances was communi- 

 cated to the Governor as the law required, but it was not published, and the matter was incorporated in 

 the Tolomes cited. 



