•i78 CRETACEOUS LAMELLIBRANX'HIA. 



1905. EsoGYRA LATERALIS, T. Wefjiier. Zeitschr. d. dcutsch. geol. GesoUsch., 



vol. Ivii, J). 184. 

 ? 1907. GRYPH.f;osTREA VOMER, S. Welh'r. Cret. Pal. New Jersey, p. 455, jil. xliv, 



figs. (5— 11. 

 1909. OsTREA (Exogyra) lateralis, W. h'liijaUi. Bull. Internat. Acad. Sei. 



Craoovie (1909), 2, 

 p. 691. 

 1911. Exogyra lateralis, Frilnch. Oji. cit., Korycau. Schiclit., p. 46, fig. 210. 

 — — — K. Voijel von Falclceiiste'in. Zti'itschr. d. deutseb. geol. 



Gesellsch., vol. Ixii, 

 ]i. 561. 



Deiicription. — Shell generally rather small, usually higher than long, very 

 inequivalve. 



Left valve very convex or inflated ; the greatest convexity is between the 

 umbo and tlie postero-ventral extremity, and gives in some ca.ses the appearance 

 of a much rounded carina, l)ehind which the valve is either flattened or slightly 

 concave; sometimes there is a posterior "wing-like expau.sion. The ventral 

 margin is rounded ; the lower part of the posterior margin is often slightly 

 concave, ending above in a point. Umbo usually much incurved, and dii-ected 

 posteriorly. The ligament pit usually curves posteriorly. This valve is attached 

 posteriorly to the umljo ; the size, shape, and direction of the attached surface 

 vary in different individuals, and affect the form of the shell in the usual 

 way. The surface of the shell shows growtli-lines, and in some specimens 

 tliere are numerous, fine, somewhat irregular ridges running pai'allel to the 

 margin of the valve. In the interior of the valve a few widely separated growth- 

 ridges occur. 



Right valve operculiform, nearly flat, or concave or undulating. Umbo very 

 small, curving spirally forwards. Surface with widely separated ridges running 

 parallel to the margin of the valve. 



A^iiitic'a.—Tlui Albian and Cenomanian examples of this species were regarded 

 by Co([uand as distinct from those found in the Upper Chalk and named 0. J(dernlis 

 by Nilssou; but d'Orbigny, Geinitz, Peron, Jukes-Browne, and Heunig have 

 shown that the forms named In feral Ik cannot be separated from those which occur 

 in earlier beds {riiiKilicnlata). Peron states that on the Continent this species 

 I'anges without interruption through all the stages of the Cretaceous, from the 

 Aptian to the Danian; he also notes its wide geographical distribution. This 

 species belongs to Conrad's '• genus " G nj phxostrea ; it has been referred to 

 (rvijphxd, by some writers, but more usually to E.vogi/ra ; the left valve, except for 

 the attached surface, is often grypheate in form, while the right valve shows some 

 resemblance to E.coyijni. Pictet and Campiche consider that 0. canaliculatn is 

 closely related to Exuijijra conlca; but it seems more probable that it is allied to 



