6o4 CRETACEOUS PALEONTOLOGY. 



The surface of each valve towards the umbo is marked by fine, 

 regular, concentric costse for a distance of from five to ten milli- 

 meters from the beak, from five to eight of the costse occupying 

 the space oif one millimeter. Beyond the umbonal region the 

 surface is marked by more or less irregular concentric lines of 

 growth, which increase in number and become stronger toward 

 the outer margin O'f adult individuals. On the posterior portion 

 of the valves an arcuate, subtriangular area extending' from the 

 beak to the sub-truncate posterior margin, is more or less sharply 

 differentiated from the remaining surface of the valve by reason 

 of the greater roughness O'f the concentric lines of growth, this 

 region usually being more sharply differentiated in the left than 

 in the right valve. 



Remarks. — This species is well represented in the collection 

 by specimens from near Swesdesboro' preserving the shell sub- 

 stance. It differs from C. densata in the lower, narrower, and 

 oblique posterior truncation of the shell, and from C. cretacea 

 in its relatively shorter and higher form, in its larger size and 

 its rougher concentric lines of growth and its finer concentric 

 umbonal costas. Besides the SwedesborO' specimens the species is 

 known from New Jersey in the form of internal casts from the 

 Navesink marl. The specimen from the Navesink marl at 

 Holmdel, referred to C. spissa by Whitfield, must also be included 

 in this species. The type of C. s'pissa has apparently been lost or 

 destroyed, but it probably came from the Navesink marl of the 

 Crosswick Creek section and was probably also a member of this 

 species. 



Formation and locality: — ^Marshalltown clay-marl, near 

 Swedesboro (177); Navesink marl, Arneytown (Morton and 

 Conrad), Holmdel (Whitfield). 



Geographic distribtttion.—'New Jersey, Alabama, Mississippi, 

 Texas, Arkansas. 



Cyprimeria cretacea Conrad. 

 Plate LXVII., Pigs. 7-8. 



i860. Sanguinolaria cretacea Con., Jour. Acad. Nat. Sci. Phil., 

 2nd sen, vol. 4, p. 277, pi. 46, fig. 11. 



