Maryland Geological Survey 555 



late and with sharper and more numerous plications. 0. larva var. 

 falcata is readily separated by the much sharper plications, which, unlike 

 those of nasuta, persist to the umbonal region. 



Occurrence. — Matawan Formation. ? St. Georges, Delaware; 

 Gibson's Island, ? head of Magothy River, Anne Arundel County, 

 Maryland. Monmouth Formation. Head of Bohemia Creek, Delaware ; 

 Brightseat, railroad cut west of Seat Pleasant, Brooks estate near Seat 

 Pleasant, 1 mile west of Friendly, and MaNeys Corners, Prince George's 

 Count}', Maryland. 



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

 vey, 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 LARVA var. MESENTERICA Morton 



Plate XXII, Figs. 6-8; Plate XXIII, Figs. 1, 2 



Ostrea falcata var. B (0. mesenterica) Morton, 1834, Syn. Org. Rem. Cret. 



Group, TJ. S., p. 51, pi. ix, fig. 7. 

 Ostrea ungulata (Schlotheim) Coquand, 1869, Mon. Genre Ostrea, p. 58, pi. 



xxvi, fig. 10 (ex parte). 

 Ostrea (Alectryoniaj larva White, 1884, 4th Ann. Rep. U. S. Geol. Survey, 



p. 296, pi. xlii, figs. 6, 7 (ex parte). 

 Ostrea larva Whitfield, 1885, Mon. TJ. S. Geol. Survey, vol. ix, p. 34, pi. iii, 



fig. 7 (ex parte). 

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



p. 446, pi. xliii, figs. 9-14. 



Description. — " Smooth, contracted ; upper valve convex ; lower valve 

 flat; with about seven strong marginal plications; inner margin crenu- 

 lated." — Morton, 1834. 



Type Locality. — Shrewsbury, New Jersey. 



Shell small, thin, rather brittle, arcuate laterally, more or less auricu- 

 late as a rule ; lower valve feebly convex, upper valve flattened, both upper 

 and lower valves concentrically striated by the incrementals and radially 

 plicate; plications along convex margin vigorous, angulated or sharply 



