178 BULLETIN OF THE NEW YORK STATE MUSEUM 



related to a number of Unios, among which may be men- 

 tioned U. radiatus, U. spatulatus, and U. ligamentinus. 



U. luteolus differs from spatulatus and radiatus in the 

 number of undulations and in the area occupied by them. 

 In the first the undulations are more numerous and extend 

 over a large area ; in the two latter they are fewer and 

 occupy a very limited area close to the tip of the beak. 

 From U. ligamentinus it differs in having more undulations 

 and in having a deeper sinus. In U. luteolus the undula- 

 tions do not continue up the anterior dorsal area while in 

 U. ligamentinus they continue up the anterior area nearly 

 to the hinge-line. 



Unio radiatus, Lam. 



Fig. 4 



Beak with six undulations, the first four of which have a 

 prominent sinus about the middle. The last two undula- 

 tions are interrupted at the middle, and the portion anterior 

 to the interruption slightly overlaps the portion posterior to 

 the interruption — - the anterior portion being nearer to the 

 beak than the posterior portion. Posteriorly, each undula- 

 tion has a fine but prominent converging line. Anteriorly, 

 there are no converging lines of the usual type but the 

 undulations are rounded and continue up the anterior area 

 nearly to the hinge-line. Dorsal areas without radiating 

 lines. 



The above description is taken from a single specimen 

 of which one valve only is nearly perfectly preserved. The 

 specimen was secured by a careful search through several 

 hundred specimens of all ages and from many localities. 

 The undulations described are contained in a space a little 

 more than T V in. wide and a little more than | in. long. A 

 very sharply defined line of growth marks the boundary of 

 the space containing the undulations. Outside of this 

 boundary there are two very slight elevations of the surface 

 of the shell parallel to the undulations but I am unable to 



