420 CRETACEOUS PALEONTOLOGY. 



of the shell apparently double, being deeply emarginate or lobed 

 at the line of division between the upper and lower portions of the 

 valve. The margin of the upper division is obliquely truncate, 

 receding from below to the hinge-line, and strongly curved in- 

 ward at the central emargination. Lower section also strongly 

 lobed and somewhat rounded." (Whitfield.) 



Remarks. The specimens of this shell have only been observed 

 in a fragmentary condition sO' that the full dimensions of the 

 species cannot be determined from actual observation. The 

 largest specimen illustrated by Whitfield is 80 mm. in maximum 

 height, and its length when complete must have been 250 mm. or 

 more. In the younger individuals of the species, as well as in 

 the older portion of full grown specimens, the sharp differentia- 

 tion between the upper and lower portions of the shell is much 

 less marked than in the mature portion of the shell, the cross- 

 section of the shell near the beak sometimes being nearly circular. 

 The species is most characteristic of the Merchantville clay, but 

 a few fragmentary individuals, which seem to belong to the same 

 species, have been recognized from the Navesink marl. 



Porniation and locality. — Merchantville clay-marl, Lenola 

 (163), near Jamesburg (140), Burlington (Whitfield); Wood- 

 bury clay, near Haddonfield (183) ; Navesink marl, near Craw- 

 fords Corner (126'^), near Walnford (148^), near Jacobstown 



(ISO). 

 Geographic distribution. — New Jersey, Mississippi, Arkansas, 



Pinna rostriformis Morton. 

 Plate XXXVII., Pigs. 2-3. 



1834. Pinna Mort., Synop. Org. Rem. Cret. Gr. U. S., p. 63. 



1841. Pinna rostriformis Mort., Proc. Acad. Nat. Sci. Phil.. 



vol. I, p. 132. 



1842. Pinna rostriformis Mort. Jour. Acad. Nat. Sci. Phil., 



1st ser., vol. 8, p. 214, pi. 10, fig. 5. 

 1 86 1. Pinna rostriformis Gabb, Synop. Moll. Cret. Form., p, 



223 (166). 

 1864. Pinna rostriformis Meek, Check List Inv. Eoss. N. A., 



Cret. and Jur., p. 9. 



