552 Systematic Paleontology 



B. Radial sculpture not developed on the right valve. 



1. Left valve radially plicated with 20-25 costae persistent from the 



umbones to the margin; right valve sculptured 

 with crowded concentric laminae. . . .Ostrea tecticosia 



2. Left valve not radially plicate. Very heavy, spatulate. 



Ostrea subspatulata 



Ostrea laeva Lamarck 



= 0. ungulata Schlotheim. 



The European form differs from the subspecies developed in America 

 in the more elongate outline and the heavier, more numerous and more 

 regular plications, both upon the concave and the convex margins. This 

 tendency is so strong in some individuals that the axis of the shell may be 

 traced as a narrow divide from the umbones to the ventral margin with 

 strongly and regular plicated areas on either side, those of the concave 

 margin being a little less coarse, more numerous and more rounded than 

 those upon the convex margin. 



Ostrea larva var. falcata Morton 

 Plate XXII, Fig. 4 



Ostrea falcata Morton, 1827, Jour. Acad. Nat. Sci., Fhila., 1st ser., vol. vi, 



p. 50, pi. i, fig. 2. 

 Ostrea falcata Morton, 1830, Am. Jour. Sci., 1st ser., vol. xvii, p. 284, vol. 



xviii, pi. iii, figs. 19-20. 

 Ostrea falcata Morton, 1834, Syn. Org. Rem. Cret. Group, U. S., p. 50, pi. iii, 



fig. 5. 

 Ostrea falcata Owen, 1860, 2d Rept. Geol. Recon. of Arkansas, pi. vii, fig. 5. 

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



xxxi, figs. 11, 12 (ex parte). 

 Ostrea larva Cook, 1868, Geol. of New Jersey, p. 375, fig. 

 Ostrea larva Conrad, 1868, Ibid., p. 724. 

 Ostrea (Alectryonia) larva White, 1884, 4th Ann. Rept. XJ. S. Geol. Survey, 



p. 296, pi. xlii, fig. 8 (ex parte). 

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



figs. 5, 6 (ex parte). 

 Ostrea falcata Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 11. 

 Ostrea falcata Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, p. 444, 



pi. xliii, figs. 3-6. 



Description. — " O. falcata, testa falciformi, auriculata, tenui ; valvula 

 superiore planulata, inferiore convexa; plieis, juxta rostrum nascentibus, 



