88 INSECUTOR INSCITI.S MENSTRUUS 



Female. — Similar; head broadly brown at vertex, defining- 

 a white lateral spot; venter of abdomen whiter, the median 

 spots and sublateral subapical black patches more distinct; 

 last tarsal joint black as in the male; abdominal bands widen- 

 ing on the sides, on the penultimate segment running to the 

 tip ; last segment black. 



Larva with the air tube thick and rounded, not over three 

 times as long as wide, the pecten without detached teeth and 

 followed by a 3-haired tuft ; anal segment not ringed by the 

 plate which is incised on the side ; comb-scales in a large 

 patch, the central spine longer than the others but not stouter, 

 the scale rather evenly fringed ; upper head hairs in twos or 

 threes, lower single or double or both double. 



Type, Cat. No. 20350, U. S. Nat. Mus. 



In some specimens, especially the largest, earliest emerging 

 ones, there is a small white ring or spot on the fifth tarsal 

 joint. The white rings are generally broad, never very narrow. 



The egg is narrowly fusiform, one side flattened, smooth, 

 not angled, the ends roundedly pointed, the micropylar end 

 shortly conical and with a mucilaginous cushion ; black, shining, 

 laid singly. 



This species combines the male genitalia of abfitchii with the 

 larva of stimulans and is thus a synthetic form. In saiisoni the 

 genitalia are similar, but the larva also is that of abfitchii, 

 having a long tube with detached pecten teeth. The coloration 

 is practically identical in all of these forms. In the east there 

 are three species of this, the cantans group, indistinguishable 

 as adults. In the Sierras there are but two and they can gen- 

 erally be easily distinguished. 



This species was very common in the Yosemite Valley in 

 May, 1916. Males were seen swarming by day in dark woods 

 or, in early morning, in camp or along the road. Usually no 

 definite swarm was seen, but single males or in small numbers 

 drifting and circling about, although sometimes in fairly defi- 

 nite clusters. The females are ready biters. Larvae occurred 

 in all the pools, preferring small detached ones, though" they 

 occurred even in large pools in old beds of the river where 

 there was still a slight current. At Fallen Leaf Lake they 



