BEAKS OF UNIONID^E 1 85 



gations on the posterior dorsal area of both shells in the 

 adult state. 



Margaritana undulata, Say 



Fig. 11 



Beaks with four very prominent undulations, which are 

 angular and much elevated posteriorly, rounded and low 

 anteriorly, and each undulation with very prominent con- 

 verging lines on both dorsal areas. Posterior dorsal area 

 with several straight and continuous radiating lines; anterior 

 area with one or two slightly curved, more or less interrupted 

 radiating lines. Surface of the young shell with many 

 concentric striae which are most numerous on the summits 

 and ventral slopes of the undulations. 



The undulations of this species in connection with the 

 converging lines are essentially triangular. 



A distinct relationship of beak and other characters 

 exists between this species and M. triangulate/, and M. 

 deltoidea. 



I IThe differences between M. undulata and M. triangtdata 

 are very slight. In the former the undulations extend over 

 a larger area and are much more elevated posteriorly than 

 in the latter. The radiating- lines on the dorsal areas are 

 more numerous in triangulata than in tmdulata. 



The undulations of M. deltoidea, though very closely 

 resembling those of M. triangtdata and M. undulata, are 

 much less stout. 



The specimens of M. undulata from Norman's Kill are 

 by far the most beautiful I have seen. The general char- 

 acters of the species, with the exception of color are nearly 

 the same throughout the state. In most of the localities 

 this species is dark brown or nearly black with slight indi- 

 cations of rays of green and yellow. Those from Nor- 

 man's Kill have a brilliant green and brown ground color 

 traversed by rays of darker green and bright yellow. As a 

 rule the specimens from Norman's Kill are less stout, less 



