532 CRETACEOUS PALEONTOLOGY. 



1864. Pholadomya (Cymella) undata Meek, Check List Inv. 



Foss. N. A., Cret. and Jur., pp. 14 and 34. 

 1876. Liopistha (Cymella) undata Meek, Rep. Inv. Cret. and 



Ter. Foss. Up. Mo., p. 236, pi. 30, figs. la-ib. 



Description. "Shell transversely broad-ovate, approaching 

 subtrigonal, moderately gibbous; anterior end rounded; pos- 

 terior side narrower and a little more compressed, rounded chiefly 

 from below; base forming a regular semiovate curve; dorsal 

 margin sloping rather abruptly in front of the beaks, straighter 

 and declining more gradually behind; hinge-margins straight,, 

 and inflected so as to form, a well-defined false area both behind 

 and a little in front of the beaks, which are somewhat elevated,, 

 incurved at right angles to the hinge-line, and located a little in 

 advance of the middle of the shell. Surface ornamented by about 

 17 to 20 of the simple, rounded, rather strong, regular, concen- 

 tric undulations, which are broader than the depressions be- 

 tween, and, as it were, cut by the radiating linear furrows, on 

 the central region of each valve, into about the same number of 

 much smaller, simple, radiating costae, less than, or nearly equal- 

 ing, the furrows by which they are separated." (Meek.) 



The dimensions of the only specimen observed, a left valve,, 

 are: length, 16.5 mm.; height, 12 mm.; convexity, 3.5 mm. 



Remarks. This species is represented in the New Jersey col- 

 lections by a single individual which agrees very closely with 

 Meek's description and illustration of the species. In only one 

 respect is there any marked difference, and that probably not 

 essential, the number of fine radiating, linear furrows being 

 greater and occupying a wider space on the central portion of the 

 shell. About 30 of these furrows can be clearly distinguished 

 and exceedingly faint ones seem to extend still further towards 

 the posterior and anterior extremities. The shell is associated 

 with C. bella, but is clearly distinct from it by reason of the 

 much finer radiating markings, and there are no intermediate 

 forms connecting the two species. 



Formation and locality. Wenonah sand, near Marlboro 

 (I30 1 ). 



Geographic distribution. New Jersey, South Dakota. 



