234 PALAEONTOLOGY OF NEW JERSEY. 



the beaks. These hitter are very large, prominent, moderately distant, and 

 inclined forward, but not much incurved, and are placed considerably in 

 advance of the middle of the shell. Body of the valves very ventricose, 

 becoming almost inflated on the umbones, and destitute of anj^ angulation 

 in the posterior umbonal region. Anterior end moderately projecting and 

 narrowly rounded; posterior end more broadly rounded, and the l)asal line 

 forming a segment of a regular ellipse. Surface of the casts destitute of 

 plications when found in hard marl, except faint indications of those seen 

 just at the margin along the basal line. On casts from the softer marls, 

 where they partake partially of the exterior characters, they show from 

 twenty-two to twenty-six radiating ribs, which are Bari'ow and sharp, with 

 much wider interspaces; and in these specimens the beaks are sharper and 

 incurved, being nearly in contact. On the internal casts the muscular 

 scars are small, but rather well marked. 



This species is somewhat smaller than C. perantiqua Conrad, and dift'ers 

 from it in its finer ribs, of which there is a greater number, that one having 

 from sixteen to eighteen. They are apjiarently associated together in the 

 same layers, and will generall}' be looked upon as one unless where care- 

 full)^ studied; but in the condition in which the external ribs are shown 

 these are so much finer that there will be little difficulty in separating tliem 

 It is possible they ought to be considered only as varieties of the one 

 species, but I have seen no intermediate forms as yet to connect them. 



Formation and localiiy. — In the topmost layer of the Uj^per Green Marls 

 at Squankum and Shark River, New Jersey (Eocene). 



Genus CEASSATELLA Lam. 



Crassatella alta. 



Plate XXIX, Fig. 17. 



Crassatella alta Conrad. Poss. Shells of tlie Tertiary, p. 31, PI. VII. Am. Jour. Sci., 

 2(1 ser., Vol. I, p. 395, PI. Ill, Fig. 1. Am. Jour. Conch., Vol. I, p. 10. 

 Check-list, Eocene, p. 5. 



A single very imperfect cast which appears to be of this species 

 occurs in the collections from Shark River. Its erect form, prominent and 

 nearly central beaks, and slight posterior umbonal angle all agree well 



