164 
IOWA ACADEMY OF SCIENCES. 
more than one* fourth the diameter of a crystalline lens. It is 
situated near the median line, about midway between lower half 
of eye and the posterior margin of the head. 
The antemisB are moderately developed, the setae reaching 
nearly to the posterior margin of the shell. The first joint of 
the setae is longer than the second. 
The post abdomen is rather slender, tapering toward the pos- 
terior end, and is armed with about fifteen strong curved spines, 
which become gradually smaller anteriorly. Anal claws are 
pectinated, and armed with a strongly developed basal comb of 
two groups of spines of about six in each group. Spines of 
upper group much smaller than those of lower. Processes of 
the post abdomen are separate, first longest, not haired, second 
and thii d haired. 
Some measurements are as follows: 
Length 
2,30 mm. 
Height 
1.32 
mm. 
Length 
2.00 mm. 
Height 
1.27 
mm. 
Length 
2,77 mm. 
Height 
185 
mm. 
Depth of head 
1.00 mm. 
Length of head 
.46 
mm. 
Depth of head 
1.07 mm. 
Length of head 
.50 
mm. 
Depth of head 
.88 mm. 
Length of head 
.44 
mm. 
Posterior spine, .70 mm. to .77 mm. 
The species is evidently very closely related to D. minnehaha, 
Herrick, and may have only varietal rank. 
The general outline of the body of old females is similar to 
that of D. minnehaha, including the angle or projection in. front 
of the brood chamber. None of the specimens examined 
showed any evidence of teeth upon the dorsal angle as are 
present in males and young females of D. minnehaha. No 
broad projection on the dorsal margin above the base of the 
antenE 80 is mentioned in descriptions of D. minnehaha or fig- 
ured in the drawings. The beak is longer in D. hybus, and is 
slightly curved toward the end. The eye in D. hybus is farther 
from the front margin of the head, and the lenses much larger 
than are figured in D. minnehaha. The posterior spine is 
longer in D. hybus. In D. minnehaha “the anal spines are 
eleven or more in full grown females, and decrease only mod- 
erately upward.” In D. hybus the anal spines vary from about 
fifteen to nineteen. Herrick says of T>. minnehaha: “ The size 
is small but variable; 1.8 mm. is a common measurement.” In 
addition the following measurements are given: “Female, 
length, 1.44 mm.; spine, .33 mm.; head, .26 mm.; depth of 
