AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 237 



ular series of high, scantily wooded ridges and rocky gulches transverse to the length 

 of the lake. Further back the peaks of the higher mountains rise bare and steep. 

 This Mission Range diminishes in height northward, and falls away to Swan River, 

 near the northeast part of the lake, but across the river to the east and north the 

 Kootenai Range continues far up along the Plathead. Opposite Mission Range, on 

 the western side of the lake, lies a mass of heights between mountain and hill, rising 

 one above another, mostly wooded, but with occasional park-like openings. Above the 

 lake a level valley several miles wide, partly densely wooded and partly prairie, extends 

 above Kalispell, and to the south lies the naked plateau of the Flathead Reservation. 



The principal tributaries are the Flathead, a still, broad river, larger than the 

 Yellowstone at the lake, running from Demersville, most of the way between flat, low 

 banks; the Big Fork or Swan River, a rocky stream, whose course from Swan Lake to 

 the Flathead is an oft-repeated alternation of wild rapids and comparatively quiet 

 reaches; and Dayton Creek on the west, which 1 did not see. The outlet (Flathead 

 River) flows rapidly away from the lake between bluffy banks which presently become 

 a canon. 



Although this lake lies in a great trough-like valley, the level of much of which is 

 not far above that of the lake itself, there is scarcely any swampy ground in its vicin- 

 ity, or weedy standing water connected immediately with it or with its tributaries 

 in the vicinity of the lake. The principal breeding-grounds offish, in fact, appear to 

 be upon these streams at a considerable distance from Flathead Lake, so that for most 

 of the species there is a long migration period. 



Our systematic work in the lake was all done in and about the northeast bay in 

 the vicinity of the mouth of the Big Fork, and at the lower end near the outlet. 



While on this bay we were the guests of Mr. K. L. Harwood, of Demersville, and 

 of the Helena Rod and Gun Club, whose club-house on the bay was our home, while 

 a steam launch belonging to members of this club afforded the only possible means 

 of access with our apparatus to the deeper waters of the lake. 



At this locality, where we remained from the 20th to the 22d of September, two 

 dredgings were made, the first beginning at 70 feet and continuing to 125 feet, and 

 the second beginning at 125 feet and continuing to 153 feet. The surface net was 

 hauled from 8 a. m. to 9 p. in., in deep and shallow water, and collections were made 

 with nets and by hand alongshore, among the weeds, from driftwood, and from stones. 



Our only temperature observations were made at noon of a bright day (September 

 22), with a common thermometer only, as no deep-sea thermometer was furnished for 

 this trip. At this time the temperature of the air was 70 F., that of the water at 

 the surface 68, and that of the mud brought up in the dredge, in a haul commencing 

 at 125 feet and stopping at 153 feet, was 42. 



At the lower end of the lake a heavy storm made work difficult, but we searched 

 thoroughly a rocky flat at the outlet, and collected from the masses of weeds washed 

 up by the waves and from the weedy shallows along the southeast shore. 



The open-water collections in Flathead Lake were very similar in general charac- 

 ter and in the relative numbers of the principal groups to those in Yellowstone Lake, 

 but the species were all different. In the former lake the so called Daphnia yulcx 

 was not once seen, but this species was replaced by A Duphnin allied to hyalina, and 

 here described as thorata. This eutomostracau made probably four-fifths to nine- 



