De cara eT ap 
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. 
