OF DENISON UNIVERSITY. 
33 
Productus dclorosus^ Win. , is apparently a synonym for P. truncatus^ 
H., and has not yet been certainly identified within our limits. 
T,ypical ventral valves of P. shumardianus are frequent in the 
sandy parts of conglomerate I, though never found much above this 
horizon. A dorsal valve apparently of this species was found in the 
nodules at the foot of the exposure at Moot’s run, at least 50 feet be- 
low the horizon of conglomerate L I quote Hall’s description. 
Shell concavo-convex, sub-hemispherical, wider than long • 
hinge-line nearly or quite equalling and sometimes greater than the 
shell below. Ventral valve very convex, gibbous in the middle and 
on the umbo, which is abruptly narrowed toward the beak, and the 
apex curved over the hinge-line; the sides abruptly depressed toward 
the cardinal extremities, which are flattened and more or less auricu- 
late. In one specunen observed, the apex is minutely truncate, and 
there is a barely perceptible line at the junction of the two valves, 
which indicate an area. Dorsal valve concave, often corresponding 
essentially with the ventral valve^ but sometimes nearly flat in the up- 
per and central portions and abruptly deflected toward the margin. 
Surface of the ventral valve 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 base of the 
spines. * The entire surface is marked by close concentric 
undulating striae.” 
The cardinal process of the dorsal valve is bifurcate. Figs. 6, 6a, 
6b and ii, of Plate XII, illustrate various conditions of this species. 
Fig. 6 especially resembling P. spinulicostatus. 
[Productus concentricus , H ] 
(Plate VI, Fig. 16.) 
(— P. shumardiana, H. ?) 
The identification of this dorsal valve was suggested by Prof. A. 
Winchell, but it is made with some hesitation, as the specimen was 
found associated with P. shumardianus as above indicated. In mark- 
ings, both concentric and pustulose, the valve agrees better with that 
species from which it seems to differ somewhat in form. Nodules, 
foot of expo.sure at Moot’s run. 
