-RHYACOPHILIDA. 
bordering the mouth parts, where it shades into brown. The 
mandibles are black and differ in form, as in figure 185. The 
labrum is small and is very weakly chitinized. 
RHYACOPHILA FUSCULA. 
184. Larva. Head and thorax. 187. Larva. Prolegs, ventral view. 
185. Larva. Mandibles. 188. Larva. Frons. 
186. Larva. Drag-hook. 189. Larva. Prolegs, lateral view. 
The Thorax.—tThe chitinous dorsum of the prothorax is straw 
yellow, marked with dark-brown, as in figure 184. Each epister- 
num is extenuated forward into an upturned spine-like projection 
which bears a seta at its tip. The ventral surface is free from 
chitinous plates and is without a horn. 
On the meso- and meta-thorax dorsal chitinous plates are lack- 
ing. The pleural sutures are deeply sunken, giving a bulbous 
form to the bordering integument above the bases of the coxe. 
The Abdomen.—The abdomen is somewhat flattened and the 
sutures are deeply constricted, giving a decidedly corrugated ap- 
pearance. External gills are entirely absent—spacing-humps and 
lateral fringe are lacking. The drag-hooks are well developed ; 
each movable claw, figure 186, has three teeth and two prominent 
sete on its lower surface; above the claw just back of the hinge 
there is an obtuse chitinous projection, figure 189, and at the base 
of each proleg there is a long rapier-like projection, figure 189; 
8 113 
