560 Systematic Paleontology 



OSTKEA TECTICOSTA Gabb 



Plate XXIV, Figs. 2-4 



Ostrea tecticosta Gabb, 1860, Jour. Acad. Nat. Sci., Phila., 2d ser., vol. iv. 



p. 403, pi. lxviii, figs. 47, 48. 

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



p. 6. 

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

 Ostrea tecticosta Coquand, 1869, Mon. Genre Ostrea, Terr. Cret., p. 50, pi. 



xvii, figs. 10, 11. 

 Ostrea pusilla Gabb, 1876, Proc. Acad. Nat. Sci., Phila., p. 321. 

 Ostrea tecticosta White, 1884, 4th Ann. Rept. U. S. Geol. Survey, p. 301, pi. 



1, figs. 3, 4. 

 Ostrea tecticosta Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 33, 



pi. iii, figs. 1, 2. 

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

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



443, pi. xliii, figs. 18, 19. 



Description. — "Elongated, irregularly oval, arcuate; beaks acuminate, 

 ligament area triangular, oblique ; muscular impressions rather large ; 

 lower valve generally attached, deep, usually deepest along the median line, 

 but becoming flattened towards the basal margin ; surface marked by 

 numerous prominent, imbricating ribs, radiating from the middle line 

 and not from the beaks; upper valve not so deep as the lower; surface 

 only marked by the usual lines of growth : upper half of the internal 

 margins of both valves denticulate, corresponding in the lower valve with 

 the external plications." — Gabb, 1860. 



Type Localities. — Tennessee and New Jersey. 



Ostrea tecticosta Gabb is well characterized by the twenty to twenty- 

 five sharp, concentric lamellae of the lower valve and the corrugations 

 radiating from the median horizontal, slightly more crowded on the 

 ventral margin, gradually becoming finer toward the dorsal margin, 

 irregular only in the region of the scar of attachment. The muscle scar 

 is large, ovate or semi-elliptical and posterior in position. The upper 

 valve is smaller than the lower, flattened and ovate-cuneate in outline. 

 Its external surface is sculptured with fine-edged concentric lamella? 

 similar to those developed on the lower valve but more crowded. The 



