562 Systematic Paleontology 



which is turned downwards at an obtuse angle; somewhat foliaceous 

 externally; muscular impression placed very near the base." — Forbes, 

 1854. 



Type Locality. — Lewis' Creek, South Washington, North Carolina. 



Shell large and very heavy ; increasing, Unio-like, in thickness toward 

 the umbones; outline ovate, subspatulate, the curvature along the hori- . 

 zontal axis much higher on the inner surface than on the outer, because of 

 the thickening toward the dorsal margin ; inner surface in some individuals 

 almost flat, in others deeply convex, the margins upturned in both the 

 horizontal and vertical planes; component layers of shell very distinct 

 when the external surface is slightly decorticated, as it almost invariably is 

 in the fossil oysters ; ten or twelve such layers discernible in a rather large 

 left valve, much more closely spaced toward the ventral margin ; prismatic 

 texture very obvious, the prisms set normal to the surface of the shell ; 

 umbines conspicuous by reason of their solidity, subcentral, orthogyrate 

 or opisthogyrate, sometimes directed almost at right angles to the hinge 

 line by reason of the increment in the umbonal region ; hinge area usually 

 wider than high, the medial area more produced ventrally, wider than 

 either of the lateral areas, cut off from them by the slightly raised mar- 

 gins and the change in the direction of the growth lines; muscle scar 

 large, pyriform, concentrically striated, placed in front of the horizontal 

 flexure, its maximum dorsal extension below the median horizontal, its 

 maximum anterior extension approximately coincident with the medial 

 vertical. 



Ostrea subspatulata Forbes is very rare in Maryland. It is an unusually 

 well characterized species, especially for an oyster, and stands apart from 

 all the co-existent species by reason of its large size, spatulate outline and 

 heavy umbones. 



Occurrence. — Monmouth Formation. Brooks estate near Seat Pleas- 

 ant, Prince George's County. 



Collections. — Maryland Geological Survey, New Jersey Geological Sur- 

 vey, IT. S. National Museum. 



Outside Distribution. — Matawan Formation. ? Wenonah sand, New 

 Jersey. Pee Dee Sand. Exogyra costata zone. Extreme top of zone, 



