532 CRETACEOUS PALEONTOI.OGY. 



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 costas, 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. hella, 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 



(130^)- 

 Geographic distribution. — New Jersey, South Dakota. 



