302 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



Viewed from above, the shell is sub-elliptical with pointed extremi- 

 ties. The cephalic extremity is more sharply pointed than the caudal. 

 The sides are convex. The hinge-line throughout the greater part of 

 its course is straight, but near the cephalic extremity of the valve 

 there is a slight sinuosity. Viewed from below the shell has 

 the same general appearance as when viewed from above. The con- 

 tact line is quite sinuous. 



The antenna of the female is five jointed. Near the distal extremity 

 of the inner margin of the second joint there is a long seta, which ex- 

 tends about to the base of the fifth joint. Near the proximal extremity 

 of the inner margin of the third joint there is the usual biarticulate 

 olfactory hair. Near the proximal extremity of the outer margin of 

 the same joint arises a long seta which extends almost to the base of 

 the next joint. From the distal extremity of the inner margin of this 

 joint there arise one long and one short seta. The long seta reaches 

 way beyond the tip of the fifth joint, while the short one does not 

 reach to the extremity of the fourth joint. From the middle of the 

 inner margin of the fourth joint there arise one long and one short 

 seta. The long seta extends to beyond the tip of the terminal joint 

 while the other extends to a little beyond the base of the same joint. 

 From the middle of the outer margin of the fourth joint there arises a 

 short seta which extends to about the base of the next joint. The tip 

 of the fourth joint bears two long and one short claw. The two long 

 claws are stout and are longer than the combined lengths of the last 

 two joints. The short claw is only about twice as long as the terminal 

 joint. From the tip of the fifth joint there arise one long and one 

 shorter claw. The shorter claw is about two- thirds as long as the 

 other claw. The tip of this joint bears also a biarticulate sensory 

 filament. 



The antenna of the male is six-jointed. In structure and append- 

 ages the first three joints resemble the corresponding portion of the 

 female antenna. From the distal extremity of the fourth joint arise 

 two peculiar biarticulate sensory filaments which extend to beyond 

 the tip of the terminal joint. From the distal extremity of the outer 

 margin of this same joint arises a short seta which extends to about 

 the tip of the fifth joint. From the distal extremity of the fifth joint 

 arise two long curved claws and one medium seta. The claws, which 

 are of equal length, are longer than the combined lengths of the last 

 three joints. The claws arise from the outer portion, while the seta 

 springs from the inner angle of the margin. The seta is about one- 

 half as long as one of the claws. From the distal extremity of the 

 sixth joint there arise one long terminal claw and one biarticulate 

 sensory seta. The claw extends to the tips of the claws that spring 

 from the fifth joint, but the seta extends less than half so far. 



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