OF DENISON UNIVERSITY. 
21 
radiating costae which bifurcate irregularly and are pustulose by the 
prominences bearing the long spines, which latter cover the entire sur- 
face though much more numerous upon the ears ; ■ surface also orna- 
mented by very numerous minute concentric striae, also in certain 
conditions of preservation by the usual fine pores; surface rarely also 
rendered irregular by large concentric folds. 
Dorsal valve plane nearly to the margin, then suddenly deflected 
to apply to the marginal portion of the ventral valve, marked like the 
opposite valve, but less distinctly upon the plane portion. Transverse 
diameter of specimen of medium size, 26 mm., length, 21 mm., con- 
vexity, 8-9 mm., projection of beak beyond hinge, 2 mm., nine costae 
in distance of i cm. at front; depression of dorsal valve (nearly at 
right angles to plane of valve) at front, 6 mm. 
A considerable suite of this species was collected at Alexandria, 
O., in light silicious flags some distance below the concretionary layer 
at Moot’s run, in connection with P. shumardianus of the same type 
as found in the concretions. 
In many respects this form resembles P. newberryi, Hall. Di- 
rect comparison with specimens from the original locality make it ad- 
visable not to separate this as a distant species. 
PRODUCTUS DUPLICOSTATUS. Win. 
(Plate XI, Figs, 26, 29.) 
“Shell rather large, with sub-circular outline, ventral valve very 
ventricose and greatly arched, with steep slopes to the right and left 
margins, not enlarged at the aperature and entirely destitute of mesial 
sinus ; marked with numerous interruptedly and irregularly striate sin- 
uous ribs, which dichotomize one or twice in the middle region of the 
valve, and toward the front resolve themselves each into a fascicule of 
three or four smaller ribs, themselves raised into a wider rib-like eleva- 
tion around the anterior margin. The tubular spines are scattered 
over the whole exterior, but become much more numerous at the 
commencement of the marginal cosate ridges. The whole exterior of 
the cast is marked also by oblique punctations, which are placed most- 
ly in irregular lines between the ribs. Length, 1.19, breadth, 
1.24, convexity of ventral yalve, .58, number of marginal ridges, 
15-20.” 
