60 
The nymph measures 24 mm.; the abdomen, 14 mm.; the 
hind femur, 4 mm.; width of head 5 mm., of abdomen 7.5 mm. 
Body sparsely covered with clavate hairs and minutely 
pointed blackish granulations; 3d joint of antenne very flat, 
oval. Labium short, meeting in front a posteriorly directed 
fringe of hairs growing under the edge of the labrum. Lateral 
spines on 7 to 9, those of 9 half as long as segment 10 at mid- 
dle. Dorsal hooks on 3-9, very low and broad with decurved 
apices. Lateral abdominal appendages about three fifths as 
long as the subequal superior and inferiors, 
3. Diastatomma sp. (a). 
Nymphs taken by Mr. Hart from gravelly shallows of the 
Ohio River at Golconda, in southern Illinois, October 27, differ 
from those of carolus in having lateral spines on the 6th 
segment of the abdomen. ; 
The nymph measures 25 mm.; abdomen, 15.5 mm.; hind 
femur, 4 mm.; width of abdomen 8 mm., of head 5.2mm. Color 
(an alcohol) yellowish with black points at top of thoracic 
sutures and a pair each side of each dorsal hook ; scars brown- 
ish. Body moderately hairy, lateral spines on abdominal seg- 
ments 6 to 9. Dorsal hooks on 2 to 9, large and subcultriform 
in front, regularly decreasing to a rudiment on 9; superior and 
inferior abdominal appendages long, laterals very little shorter. 
V. Haaentus Selys. 
There is but one North American species of this interest- 
ing genus, the flat nymph of which is conspicuously unlike that 
of any other dragon-fly in form, as described below. It is found 
clinging to the flat surfaces of driftwood and stones or amongst 
dead leaves. The Hphemeride inhabiting such surfaces are also 
conspicuously flattened. They are therefore not easily picked 
off by fish nor dislodged by a rush of water, and are able to slip 
away through narrow crevices. Perhaps Hagenius has this 
shape for similar reasons. Its blackish color is evidently pro- 
tective. 
