366 CRETACEOUS LAMELLIBRANCHIA. 



1906. Osteea (Gryph^ea) vesicularis, M. Boide and A. Thevenin. Annal. 



Paleont., vol. i, p. 49 [7], pi. ii, fig. 3. 

 ? — Gryph^a vesicularis, J. Pethi't. Palseontographica, vol. lii, p. 188, pi. 



xii, figs. 2, 3. 



1907. convexa, 8. Weller. Cret. Pal. New Jersey, p. 451, pi. xlv. 



1910. vesicularis, F. Freeh. Neues Jahrb. fur Min., etc., i, p. 6, 



pi. ii, fig. 1. 

 ? — Ostrea vesicularis, H. Briiygen. Ibid., Beil.-Band xxx, p. 744. 



1911. — hippopodium, A. Fritsch. Stud, im Geb. bohmisch. Kreideformat., 



Korycaner Schiclit., p. 48, fig. 217. 

 V — Grtphea vesicularis, M. E. Tadusz. Mitteil. Jahrb. ungarisch. geol. 



Reichsanst., vol. xix, p. 110, 

 pi. iii, fig. 3. 



— Ostrea hippopodium, W. Roycda. Bull. Internal.. Acad. Sci. Cracovie, 



p. W7. 

 — K. Voyel von FalcJcenstein. Zeitschr. d. deutscb. 



geol. Gesellsch., vol. 

 lxii, p. 558. 



— Grtphea vesicularis, v. Falelenstein. Ibid., p. 560. 



Non 1859. Ostrea vesicularis, T. Wiltshire. Eed Chalk of England (Geol. Assoc), 



p. 16, pi. ii, fig. 5. 



Description. — The left valve, when attached by only a very small part of the 

 nmbo, has a grypheate form, being usually very convex, and with the umbo 

 prominent and incurved ; the outline of the valve is rounded, but the posterior 

 part is more or less produced ; the postero-dorsal part is often convex and some- 

 times distinctly limited from the remainder of the valve ; this convex part when 

 strongly developed may be produced backwards in a wing-like form. In large 

 specimens of the grypheate form this valve becomes very thick. 



When the left valve is attached to a larger surface of more or less rounded 

 outline it is still grypheate in form, but with the umbonal region truncated owing 

 to the attached surface being flat or concave. When the attached surface is still 

 larger, relatively to the entire shell, the free marginal part possesses the same 

 character as the corresponding part of the grypheate form, and this free part 

 grows upwards from the attached surface. When nearly all the valve is attached 

 then only a narrow rim grows upwards at the margin ; lastly, in some cases the 

 entire valve is attached so that the whole of it is flat or concave ; in the interior 

 of such forms a few distinct concentric ridges are often found at intervals, and 

 from the outermost of these the marginal part of the valve becomes gradually 

 thinner and usually shows a porous structure. 



When the left valve is attached to a cylindrical or other elongate object, the 

 form of the shell depends on the direction of the long axis of the attached surface. 

 If the axis is nearly perpendicular to or forms a considerable angle with the plane 



