MAEYLAND GEOLOGICAL SURVEY 381 



thin flat lamellse; margins near the beak transversely denticulated or 

 striated. 



This is one of the species named by Conrad and published by Co])e 

 (he. cit.) that has never been described. The original specimens from 

 Charles county are in the Academy of Natural Sciences in Philadelphia. 



This shell is closely allied to the upper Oligocene varieties of 0. sellce- 

 formis and may be considered an early Miocene variety of the same 

 species. 



Length, 58 mm.; Avidth, 43 mm.; diameter, 15 mm. 



Occurrence. — Calvert Formation. Charles county near the Patux- 

 ent river (Cope) ; Plum Point, Truman's Wliarf, Chesapeake Beach, 

 3 miles south of Chesapeake Beach. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. N"ational Museum, Philadelphia Academy of Natural Sciences. 



Ostrea trigonalis Conrad. 

 Plate CI, Figs, la, lb. 



Oittrea trir/onalis Conrad, 1854, Wailes' Kept. Agric. and Geol. Miss., p. 289, pL xiv, 



fig. 10 (name and figure only). 

 Ostrea trigonalis Conrad, 185.5, Proc. Acad. Nat. Sei. Phila., vol. vii, p. 259. 

 Oatrea trigonaUs Dall, 1898, Trans. Wagner Free Inst. Sei., vol. iii, pt. iv, p. 681. 



Description. — " Triangular, fiat, surface irregular, with some indis- 

 tinct radiating lines; muscular impression obliquely suboval, situated 

 nearer the summit than the base; margin somewhat ascending, sub- 

 margin earinated." Conrad, 1855. 



" The species is wide spread and recognized by its flat upper valve, 

 few-ribbed lower valve, straight hinge line, flat hinge area, with exca- 

 vated central channel and the peculiar vermicular sculpture of the sub- 

 margin on each side near the hinge line." Dall, 1898. 



Length, 90 mm. ; width, 70 mm. 



Occ^irrence. — Choptank Formation, Jones Wharf, Greensboro 

 (rare in Maryland). 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Ostrea carolinensis Conrad. 

 Plate CI, Figs. 2, 3, 4. 



Ostrea Carolinensis Conrad, 1832, Fossil Shells of the Tertiary, p. 27, pi. xiv, fig. 1. 

 Ostrea carolinensis Dall, 1898, Trans. Wagner Free Inst. Sei., vol. iii, pt. iv, p. 686. 



