374 THE CANADIAN ENTOMOLOGIST 



during the second half of July, and in August, 1913, and obtained 

 plenty of the nymphs from two or three small ponds at Rock City, 

 a village near the Biological Station. From these a number of 

 adults emerged on July 20 and 21. 



Most of the adults taken have the legs entirely or almost 

 entirely black and agree with Ris's description of 5\ obtriisum 

 morrisoni. They intergrade, however, with pale-legged specimens 

 and are undoubtedly conspecific with 5. pajlipes, as Ris himself 

 suspected. But I cannot consider them as a variety of obtrusum, 

 for, in the first place, I found both pallipes and typical obtrusum, 

 in every respect like eastern specimens, at Okanagan Landing, 

 B. C, on the Pacific Slope, while pallipes ranges eastward to Water- 

 ton, Alta., In the second place, the nymphs of pallipes are quite 

 distinct from those of obtrusum, but are so extremely like those of 

 costiferum as to be practically indistinguishable from that species. 

 I have neglected to rear S. obtrusum and have no nymphs that I 

 can refer to it with certainty, but I have a number of 5. rubicun- 

 dulum, which Professor Needham was unable to distinguish from 

 obtrusum, and they are very easily separated from pallipes. 



The nymphs of pallipes like those of rubicundulum frequent 

 small stagnant pools or ditches, while costiferum seems to prefer 

 shallow reed-grown parts of ponds or lakes. 



Nymph (pi. XXV, figs. 6-8). — Eyes moderately prominent, later- 

 al margins of head very oblique, passing into the posterior margins 

 without any semblance of an angle. Mentum of labium narrow 

 at base, the basal breadth being somewhat less than one-fourth 

 the greatest breadth, which is almost equal to the length; sides 

 moderately concavely curved, diverging in the distal fourth at an 

 angle of about 90°, median lobe depressed at an angle of about 30° 

 with the general surface of the mentum. Mental setae 13-14, the 

 4th or 5th from the side longest. Lateral setae 10-11. Movable 

 hook slender, one-fourth to nearly one-third as long as the distal 

 margin of the lateral lobe, the latter with very low crenulations, 

 at the intervals between which are groups of 3 (sometimes a rudi- 

 mentary fourth in some of the groups) successively longer setae, 

 the third much longer than the other two (see fig. 8). 



Abdomen widening gradually from base to segment 6, narrow- 

 ing more rapidly caudad, especially on segments 9 and 10. Dorsal 



