Si8 CRETACEOUS PALEONTOLOGY. 



the concentric markings of that portion of the shell which is 

 preserved. The dimensions of the restored type are : length, 37 

 mm.; height, estimated, 20 mm.; thickness about 7.5 mm. 

 Beaks incurved and nearly or quite in contact, situated back of 

 the middle of the shell, pointing backward. Antero-cardinal mar- 

 gin straight and nearly horizontal in front of the beaks, curving 

 downward in front; anterior margin rounding from the cardinal 

 into the basal margin; basal margin slightly convex in the 

 middle, curving upward in front and behind; posterior margin 

 apparently rounded. Valves most prominent below the umbonal 

 region, the surface curving rather abruptly to the cardinal mar- 

 gin, gently convex to the anterior and ventral margins; pos- 

 teriorly the valves are rather abruptly depressed along" a line 

 running obliquely backward from the beaks, so that the postero- 

 cardinal portion of the shell is conspicuously compressed. Sur- 

 face of the shell marked by rather strong concentric undulations 

 and by fine concentric lines of growth ; the postero-cardinal com- 

 pressed portion of the shell is apparently smooth, but the char- 

 acter of the markings of this portion of the shell is not clearly 

 shown on the specimen. 



Remarks. — This species is much like A. jersey ensis, but it is 

 proportionally more elongate and not so high. It is also marked 

 by the conspicuous, somewhat regular, rounded, concentric un- 

 dulations which are wanting in the other species. 



Formation and locality. — Merchantville clay-marl, near James- 

 burg (139, 140). 



Geographic distribution. — New Jersey. 



Genus Cercomya Agassiz. 



Cercomya peculiaris (Conrad). 



Plate LVL, Figs. 13-14. 



1869. Inoceramus peculiaris Con., Am. Jour. Conch., vol. 5, 



p. 43, pi. I, fig. 13. 



1870. Cercomya peculiaris Con., Am. Jour. Conch., vol. 6, p. 76. 

 1886. Cercomya peculiaris Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 178, pi. 23, figs. 24-25. 



