LAMBLLIBEANOHIATA OF THE LOWER MARLS. 103 



the shell. Posterior hinge-line long and straight; anterior end truncate 

 and at right angles to the postero-cardinal line; basal line ventricosely 

 convex, more sharply rounded near the anterior truncation; posterior 

 extremity of the valves narrowly rounded. Anterior slope vertical, or nearly 

 so, forming an angulation which extends from the beak to the antero-basal 

 margin; postero-cardinal slope abruptly rounded. Surface of the shell 

 marked by fine concentric lines, and a few distant varices of growth; no 

 radiating striae can be distinguished on the surface. Posterior hinge with 

 about twenty sharp, somewhat recurved teeth; anterior side not observed; 

 ligamental pit moderate in size. 



This species differs in shape from any American Cretaceous species yet 

 described. It approaches most nearly N. distprta Gabb (Jour. A. N. Sci., 

 Phil., new series, Vol. IV, p. 396, PI. LXVIII, Fig. 34), from the Ripley group 

 of Tennessee, but is much less distinctly triangular, and does not possess 

 the radiating lines of the surface as in that shell. 



Formation and locality. — In the white limestone nodules of the lower 

 Cretaceous marls at Marlboi'ough, N. J. A second specimen, rather more 

 curved on the postero-cardinal margin, occurs in the collection of the 

 Academy of Natural Sciences of Philadelphia, from Haddonfield, New 

 Jersey, in soft micaceous sand. 



Nucula Slackiana. 



Plate XI, Figs, i and 3. 



Leda Slackiana Gabb. A. N. S., Pbil., 2d ser.. Vol. IV, p. 397, PI. LXVIII, Fig. 37. 



Synopsis, p. 133. 

 Nnculana Slackiana (Gabb). Meek, Checlvlist, p. 8. Geol. Surv. Kew Jersey, 18G8, 



p. 725. 

 Nncula Slackiana Gabb. Proc. A. N. S., Phil., 1876, p. 318, but doubtfully referred to 



If. percrassa Gabb. 

 ? N. percrassa Gabb. Proc. A. N. S., 187G, p. 318. 

 Not N. percrassa Courad. J. A. N. S., 2d ser., Vol. Ill, p. 327, PI. XXXV, Fig. 4. 



Shell of rather large size for the genus. General form ovate, elon- 

 gate-triangular, or subelliptical; about once and a half as long as high, 

 with the anterior end obliquely truncate, but rather long ; cardinal line 

 slightly arcuate; base gently curving and the posterior end rather sharply 

 rounded, and almost obtusely pointed near the line of the hinge. Muscular 



