452 W. B. Dwight — Wappinger Valley Limestone. 
the less conical one, and, more especially, the marked difference 
in the character of the muscular impressions. 
It is quite possible that it represents a new genus, but I will 
refer it provisionally to that one of the Discinoid genera to 
which it seems the more closely related. 
Orbiculoidea* conica, sp. nov.—Shell black and flinty, sub- 
Oo 
cylindrical and gibbous forms; apex pointed, sub-central, ele- 
vated in many specimens } a diameter or more above the mar- 
ginal plane; peduncular groove ovate, extending from } to} 
the distance from the apex to the margin, foramen at the wider 
part, i. e. at the end most distant from the apex. Dorsal valve 
either nearly flat, slightly convex, or somewhat concave ; apex 
rom ith to of a diameter distant from the nearest part of 
well-preserved, they are smoothly rounded, as are also the val- 
eys between, but slightly steeper on the apical side. 
In the best specimens of the internal markings of the flatter 
(dorsal) valve, there is a deep marginal pallial impression, and 
there are two large well-marked pyriform muscular impressions 
nearly central, diverging toward their broader portions poster 
pe x 
the above and the posterior margin and near to the latter ; these 
are however very joabtfal. The internal character of the con- 
ical ventral valve cannot be satisfactorily discovered from any 
of the specimens on hand. 
end of the exposure of Trenton, which I described Pg my last 
* D’Orbigny. 
