Classinea Subulosa, also known as the summer stone can be an important part of the trout's diet during their emergence in late summer and early fall. During this time most of the big bugs of spring and early summer have hatched, some exceptions are the October Caddis, and the Isonychia mayfly which give the trout their last prime rib dinner of aquatic insects a bit later in the fall. This species is very unique because the male has very short wings and cannot fly, the female has fully developed wings yet runs across the water to oviposit her eggs. I've seen live specimens on the lower Yuba just after emergence as they crawl around moist decomposed plant matter hiding out in search of a mate. They are elusive.
It's tough to get an ID on them as they are closely related to the Golden Stone, I've misidentified them many times myself. The easiest way to tell one from the other is the Stub Wing has a large "W" on the head, while the Golden has an hourglass shaped vertical marking on its own head. Another clue to identification is the Stub Wing has much longer antenna and tails which are darker than that of the Golden Stone. On some tail waters like the Lower Yuba their emergence can be timed as the flows are decreased from the dam.
For nymphing, high sticking the side water with a nymph that closely resembles the Stub Wing is a great tactic, size and profile count more than an exact color match when choosing a fly. These presentations should be dead drifted. For the adult, a tan stimulator skated and twitched in and below the riffles can result in some very explosive takes. Aquatic insects continuously impress me, the one rule I have learned with them, is there are no rules, only guidelines. Fresh large stonefly shucks this time of year are most likely the Stub Wing, look for clues on your next venture of your favorite river, you just may find the summer stone.