MOLLUSCA. 531 



Remarks. There seems to be no sufficient reason for separ- 

 ating these New Jersey shells from Cymella bella Con., although 

 Whitfield has established the species C. meeki for certain Black 

 Hills examples, to which species he has referred the New Jersey 

 specimens. The distinctive character of C. meeki, as indicated 

 by Whitfield, is in the presence of the radiating ribs over the 

 entire surface of the shell, while in C. bella, according to the 

 original illustration of the species, they are restricted to the cen- 

 tral portion of the shell. In all the specimens of this shell in 

 the recent collections of the Survey, these ribs are most strongly 

 developed on the central portion of the shell, becoming fainter 

 both posteriorly and anteriorly j in most instances the anterior 

 portion of the shell is entirely destitute of the ribs while faint 

 indications of them continue nearly to the post-cardinal border. 

 Although this distribution of the radiating ribs is quite differ- 

 ent from Conrad's illustration O'f C. bella, in his description of 

 that species he says "disk sculptured with concentric furrows 

 and acute radiating ribs interrupted at the furrows, anterior side 

 nearly or quite destitute of radii and occasionally exhibiting 

 minute raised points." This description fits the New Jersey 

 specimens exactly, and it is highly probable that the original 

 figure is not a fair illustration of the species. The Cliffwood 

 clay specimens from New Jersey resemble the original figure 

 of C. bella more closely than those from the higher formations, 

 but all, including also the Black Hills specimens of Whitfield, 

 should doubtless be referred to a single species, C. bella. 



Formation and locality. Cliffwood clay, near Matawan 

 (107); Merchantville clay-marl, near Matawan (101); Wood- 

 bury clay, Lorillard (102), near Matawan (103), near Haddon- 

 field (165) ; Wenonah sand, near Marlboro (I3O 1 ). 



Geographic distribution. New Jersey, North Carolina, Texas, 

 Arkansas, South Dakota. 



Cymella undata (Meek and Hayden). 

 Plate LVIIL, Fig. 13. 



1856. Pholadomya undata M. & H., Proc. Acad. Nat. Sci. Phil. 

 (1856), p. 81. 



