LAMELLIBRANCHIATA FEOM'BASE OP UPPER MARLS. 213 



SO far as I can ascertain, only in the lowest layers of the Upper Marls, asso- 

 ciated with the forms referred to the Cretaceous. It is known from Shark 

 River and Squaukum, and doubtfully from Farmingdale, New Jersey. 



CrassateUa rhombea, n. sp. 

 Plate XXVII, Figs. 16-19. 



Shell of about a medium size for the genus ; transversely liiomboidal 

 in outline and proportionally ventricose; the length rather more than one- 

 fourth greater than the extreme height. Beaks large, prominent, and rather 

 distant, situated at about the anterior third of the length. Cardinal margin 

 on the posterior side rapidly declining from the beaks to the postero-cardinal 

 angle, and in front very rapidly declining. Anterior end of the shell neatly 

 rounded from the lower margin of the lunule-like depression to its blending 

 with the regularly curved basal line. Posterior end broadly and obliquely 

 truncate, but with a slightly rounded margin, which unites with the basal 

 line without perceptible angulation. Umbonal angle scarcely marked, 

 although somewhat prominent. Surface of the shell concentrically marked, 

 and also characterized by indistinct radiating lines, which are most distinct 

 near the outer margin. About ten of the radii occupy a space of half an 

 inch on the posterior border of the shell. The largest internal cast of the 

 species which I have observed is about two and a quarter inches in length 

 by nearly one and thi-ee-quarters of an inch in height from the basal line 

 to the extremities of the filling- of the beaks. The outline of the cast is 

 transversely ovate exclusive of the projections of the beaks, and widest at 

 the posterior end, which is somewhat obliquely truncate, although slightly 

 rounded on the margin. Basal line broadly curved and the anterior end 

 narrowly rounded. Beaks situated a little anterior to the middle of the 

 length, broadly triangular in outline, and projecting- considerably beyond 

 the line of the hinge; projections thin, very distant, and not incurved, indi- 

 cating very ventricose valves with erect beaks, as shown in the example 

 which retains the shell, and which is figured on the plate. Muscular scars 

 moderately large, strongly elevated on the cast, showing deeply impressed 

 scars in the shell; pallial Hue very strongly marked. 



