-OQ K. B. VVILLIAISISON. 



9 .—Frontal vesicle tuberculute, cairving behind each lateral 

 ocellus and ending there, or continued posteriorly, in which case 

 each extremity is produced into a spine ; the carina enclosing the 

 vesicle thickened and produced on either side to form a spine be- 

 tween the lateral ocellus and the eye, this spine apparently correla- 

 ted with a small dorsal subapical hemispherical excavation on each 

 branch of the inferior appendage of the male. Vulvar lamina from 

 very short to about one-fifth as long as the sternum of 9. Appen- 

 dages longer than 10, acute. I have been unable to find a chai'acter 

 which isolates the females in question as well as the males are iso- 

 lated by the form of their superior abdominal appendages. The 

 frontal vesicle, as in amnicola, notatns and plagiatus, is similar to 

 certain other species in the genus. The posterior spines of scndderi 

 and spinicepa are better developed in brevis ; in copulation they 

 would overlap the internal edges of the branches of the inferior 

 appendage of the male. The lateral spine between the lateral 

 ocellus and the eye is common to the genus, though in such species 

 as spicatas and exilis it is reduced to the merest vestige. In general, 

 in both sexes, the eyes are more approximated than usual in the 

 genus, the vertex meets the frons in a very obtuse angle, the angle 

 of the frons is rounded and low, and the occipital crest is low, but 

 such characters, indefinite as they are, can hardly be used in isola- 

 ting the group. 



Professor Needham (Canadian Entomologist, vol. xxix. No. 7, 

 pp. 167 and 177) has characterized the nymphs of notatus, spmiceps 

 and plagiatus as follows : "Wing cases laid parallel along the back ; 

 third joint of antennae cylindric, at least twice as long as wide ; ab- 

 dominal appendages longer than the 10th segment; front border of 

 median lobe of labium straight, with the usual fringe of flat scales, 

 but without teeth ; abdomen not abruptly narrowed before the 9th 

 .segment; body spindle shaped, little flattened; fore and middle 

 tibiue with small external apical hooks, or with none; ninth abdomi- 

 nal segment one half longer than the eighth, its lateral margins 

 nearly parallel ; a minute mid-dorsal apical spine on the 9th .seg- 

 ment only; lateral lolie of the labium with a strongly incurved end 

 hook and teeth on the inner niargin increasing in size posteriorly." 



So far as known to myself the nymj)hs of the five species of this 

 subgenus live only in running water, with the exception of plagiatus 

 which is found in both flowing and still water. 



