336 NEW YORK STATE MUSEUM 
free, when suddenly they spread out fanlike and held above 1 
the surface of the shallow water, the legs all bunched up and | 
still remaining in the pupal skin. The force of the flowing 
water and the struggles of the insect in from one to five minutes 
cause the legs to draw out, and, thus liberated, the imago im- 
mediately takes flight. In deeper water the wings probably do 
not unfold till after the insect is washed to the surface, though 
no observations were made upon this. Figures of larvae and 
pupae may be found in Comstock’s Manual, and in Kellogg’s 
vapers in the Entomological News for 1900, and in Cal. Ac. Soe. 
Proc. 1903. 
Family sSImuLIIDAE 
Black flies 
In this family the body is short and stout; the legs are short; 
and the tibiae possess spurs. The antennae are scarcely longer 
than the head, cylindric and 10 jointed; the two basal joints are 
differentiated; the others are closely united. Proboscis not 
elongated, with small horny labella; palpi are four jointed. The 
thorax is much arched, giving the fly a humpbacked appearance; 
the scutellum is small; the abdomen is cylindric, composed of © 
seven or eight segments; the legs strong and not elongate. The 
wings are broad, iridescent, and not clothed with hairs. The 
veins near the costal border are stout; those on the other parts 
of the wing are very weak. [See pl.34, fig. 1] 
The larvae are soft skinned, not slender, usually more or less 
constricted in the middle. The head is cylindric, with eye spots 
on each side. The head bears two large fan-shaped organs, 
which aid in procuring the food. Respiration is accomplished 
by means of three blood gills which are pushed out from the 
dorsal surface of the last abdominal segment (Miall & Ham- 
mond say from the rectum). On the segment back of the 
head is a foot armed with hooks, and on the posterior 
end of the body is a disklike sucker by means of which the 
larva clings to the rocks or to plants. The creature moves 
about on the surface of the rocks with a looping gait similar _ | 
to that of a measuring worm, and a web is secreted which pre- 
vents its being washed away by the swiftly flowing water. 
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