170 



base and tip; the claw long and slender with a broad 

 dent near the base and with three more pointed dents 

 interiorly near the tip. Labrum transverse, its front mar- 

 gins slightly incised in the middle. 



Seven pairs of gills, the fore- 

 most and hindmost pairs of which 

 are the largest. Each gill con- 

 sists of a large lamella, in which 

 the tracheal branches are distinct, 

 WM^ — ^ ^ ^nd of a tuft of filaments, placed 

 jawv a /n, ät the base of the underside of 

 M^yJ ( \. \ > the lamella. The hind part of 

 each lamella overlaps the front 

 ^C-y. ^ .^ part of the following one. 



^' Length of body 10—12 mm, 



^^2- ^- of setæ 8 mm. 



Larva of Rh, ussingi. 



a. labium, b. right •it 



mandible, c. right The nvulct at Jcxcn IS run- 



'"ä^'"^ ning swiftly, and the bed is very 



stony. The nymphs of Rh. ussingi were found clinging 



to the underside of the stones, where the stream was 



most rapid. 



The nymphs of the genera of Ecdyuridæ may be se- 

 parated in the following way: 



1. Two caudal setæ 2 



Three caudal setæ 3 



2. Foremost pair of lamellæ enlarged, so 

 that they touch each other below the 



abdomen; hindmost pair likewise Iron. 



No lamellæ touch each other below the 



abdomen Epeorus. 



3. Foremost and hindmost pairs of lamellæ 

 placed as in Iron; basal joint of maxil- 

 lary palpus very stout Rhithrogena 



No pair of lamellæ touch each other 



below the abdomen; basal joint of maxil- 

 lary palpus slender and cylindrical 4 



