398 



CRETACEOUS LAMELLIBRAXCHIA. 



1905. ExOGYEA CouLOSi, E. Ilarhorl. Fauna d. Scliaumburg - Lippf'scheu 



Kveidemulde (Abhaudl. d. k. 

 preuss. geol. Landesanst., n.f., 

 45), p. 30. 



1907. — — 0. Hanpt. Neues Jahrb. fiir Min., etc., Beil.-Bd. 



x.xiii, p. 211. 



1908. — — A. A. Sfojanoff. Auii. gcol. et min. Russie, vol. x, 



p. 119. 



.' r. 



\^ 





Fig. 194. — Exogyra simtafa (Sow.) Ilytlic Beds, Sevenoaks. Sedgwick Museum, Cambridge. Left 



valve. X 3. 



Bescri])tion. — Shell ^\\t\\ subtrigonal, snbquadrate, oval or rounded outline ; 

 often large and massive. The posterior margin is truncated ; in the early stages of 

 growth it is either nearly straight or slightly concave ; later it becomes more 

 concave, with an angular projection at its dorsal and at its ventral end ; in large 

 specimens this margin usually becomes more rounded. The anterior and ventral 

 margins usually form a convex curve. In large specimens the postero-dorsal 

 margin is sometimes nearly straight. In many small, and in some large specimens, 

 the height of the shell is distinctly greater than the length, l)ut in others, particu- 

 larly large forms, the height and length are nearly equal. In some of the high 

 forms the shell is considerably arched, the posterior part being concave. 



Left valve moderately or very convex. Umbo often relatively small, usually 

 spiral, with a moderate or large backward curvature. The surface of attachment is 



