LAMELLIBRANOHIATA FEOM THE MIDDLE MARL BEDS. 195 



not restricted to the Middle Beds, but is perhaps more strongly marked 

 there than among the true 0. Bryani at the base of the Upper Beds. It 

 seems quite diflficult to arrange all these forms under GrypJicea vesicularis 

 Lam., and still it is very difficult to point out constant characters of differ- 

 ence. After much study of them with the other forms I am as undecided 

 in my own mind as to their true specific distinction as when I first examined 

 them, and shall tlierefore retain them as varieties. 



Formation and locality, — The particular form here indicated is associated 

 with the small round form of G. vesicularis in the yellow sands of the Middle 

 Beds throughout Monmouth County, and also particularly so in the vicinity 

 of New Egypt, New Jersey. 



Genus GRYPH^OSTREA Conrad. 



(Am. Jour. Conch., Vol. I, j). 15.) 



Gryphaeostrea vomer. 



Plate XXVI, Figs. 11 and 12. 



Gryphcea vomer Morton. Synopsis, p. 54, PI. IX, Fig. 5. Stoliczka Pal. Ind., Vol. Ill, 

 p. 457. 



Exogyra lateralis (l^eils.) Gabb. Synopsis, p. 123. Meek, Check-list, p. 6. 

 Gryphceostrea lateralis (Neils.) Meek. Geol. Sury. N. J.,1868, p. 724. 



Shell of only moderate size, narrowly elongate-oval or elongate-ellipti- 

 cal in outline, strongl}^ arcaate from beak to base, and generally more or less 

 twisted laterally. Right or lower valve deeply concave internally, and the 

 upper one flat or a very little arching with the other. Apex of the lower 

 valve distinctly twisted and often decidedly coiled, and that of the upper 

 distinctly curved anteriorly, although flat. Surface of the lower valve 

 smooth or only slightly lamellose over the larger part of the body of the 

 shell, but often strongly lamellose near the apex, and particularly on the 

 anterior cardinal portion, where it is frequently distinctly auriculate. Sur- 

 face of the upper valve marked by distant and somewhat regular, elevated, 

 concentric ridges, formed by the free margins of the lamella. Cardinal or 

 ligamental area very small or subobsolete. 



