LAMELLIBRANOIIIATA FEOM THE EOCENE MARLS. 229 



have placed this and the others under the genus Nuculana fvom the fact that 

 I have not been able to detect any ^^ largely sinuate pallial line" on any of the 

 casts, and because the cartilage pit beneath the beak is S7nall instead of 

 large. These two features appear to be about the only distinction there is 

 between Nuculana and Yoldia, and as these agree most nearly-with the for- 

 mer, which is also the oldest genus, I have adopted that name in preference 

 to the other. The cartilage pit in the present species is reduced to its min- 

 imum size, being so small as to require magnifying in order to see it dis- 

 tinctly, while the teeth near the center of the line are also extremely minute. 

 Formation and locality. — In the top layer of the Upper Green Marls, at 

 Shark River, Farmingdale, and Squankum, New Jersey. 



Genus NUCULARIA Conrad. 

 Nucularia secunda, n. Hp. 

 Plate XXIX, Figs. 13 and 14. 



Shell small, very inequilateral, transversely elongate, and very elon- 

 gate-ovate or subelliptical in outline. Cardinal and basal lines subparallel, 

 the anterior end being a little the widest. Beaks small, situated at about 

 one-fourth the length of the shell from the anterior end. Anterior extremity 

 of the shell sharply rounded; posterior end narrower and rounded; basal 

 line broadly but regularly curved ; posterior hinge-line very slightly con- 

 cave. Disk of the valve gently depressed-convex, the shell apparently 

 somewhat gaping posteriorly. Hinge-line marked by a moderately large 

 triangular pit beneath the beak, and by about eight pectenoid teeth on the 

 anterior side of the beak, and about thirteen or fourteen on the posterior 

 side; those of both parts gradually increasing in size from the beak out- 

 ward. Surface of the shell unknown. 



The shell is known only by internal casts, in which condition it very 

 closely resembles N. papyridea Conrad, from the base of the Cretaceous 

 marls at Haddonfield, N. J.; the form is, however, not quite so robust, 

 being narrower in proportion to its length, and the posterior end is 

 rounded instead of being obliquely truncate, as in that one, which gives a 



