556 Systematic Paleontology 



undulatory, not invading the medial portion of the shell, from three or 

 four to seven or even nine or ten in number; radial sculpture along the 

 concave margin reduced to marginal crenulations. Hinge area straight 

 in auriculate individuals, rostrate when auricles are not developed ; liga- 

 mentary area medial, moderately high, groove shallow ; muscle scar rather 

 small, semi-elliptical, slightly posterior in position ; inner margins undu- 

 lated in harmony with the external sculpture. 



Ostrea larva var. mesenterica is the smallest and most strongly arcuate 

 of the 0. larva group. It is best characterized by the strongly undulated 

 convex margin, the finely crenulated concave margin and non-plicate 

 umbonal region. 



Occurrence. — Monmouth Formation. Brightseat, Brooks estate near 

 Seat Pleasant, 1 mile west of Friendly, Prince George's County. 



Collections. — Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, New Jersey Geological Survey, U. S. National Museum. 



Outside Distribution. — Monmouth Formation. Navesink marl and 

 Tinton beds, New Jersey. Widely distributed in the Gulf region but not 

 differentiated. 



Ostrea plumosa Morton 



Ostrea plumosa Morton, 1833, Am. Jour. Sci., 1st ser., vol. xxiii, p. 293. 

 Ostrea plumosa Morton, 1834, Syn. Org. Rem. Cret. Group, U. S., p. 51, pi. 



iii, fig. 9. 

 Ostrea plumosa Meek, 1864, Check List Inv. Fossils N. A., Cret. and Jur., 



p. 6. 

 Ostrea plumosa Conrad, 1868, Cook's Geol. of New Jersey, p. 724. 

 Ostrea plumosa Coquand, 1869, Mon. Genre Ostrea, Terrain Cret., p. 61, pi. 



xxxii, fig. 9. 

 Ostrea plumosa Gabb, 1876, Proc. Acad. Nat. Sci., Phila., p. 320. 

 Ostrea plumosa White, 1884, 4th Ann. Rept. U. S. Geol. Survey, p. 299, pi. 



xxxvii, figs. 5, 6. 

 Ostrea plumosa Whitfield, 1885, Mon. IT. S. Geol. Survey, vol. ix, p. 31, pi. 



iii, figs. 12, 13. 

 Anomia argentaria Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, pi. iv, 



fig. 9. 

 Ostrea plumosa Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 10. 

 Ostrea plumosa Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, p. 



439, pi. xlii, figs. 16-18. 

 " Ostrea denticulifera " Weller, 1907, Ibidem, p. 436, pi. xliii, figs. 1, 2. 



(Not O. denticulifera Conrad, 1858.) 



