150 BULLETIN UNIVERSITY OF MONTANA 
forestall any of his work or enter the field he has chosen by generaliza- 
tions as to the influences which have caused the present distribution of 
the different species of forest trees. All this will be given in his final 
report, which will be published later, no doubt. 
Rost lake is a typical example of a body of water being filled in by 
sediment and having its inlets, outlet, and sides choked by hydrophytic 
vegetation. This vegetation is encroaching on the lake in every direc- 
tion. The annual rise and fall of the lake is several feet, and for a hun- 
dred feet or more in every direction from the lake the vegetation was 
profuse and abundant, at the time of our stay, early July. In the spring 
the surface of the lake is considerably larger. 
The outlet of the lake, Rost creek, carries the water into Swan river. 
The lake has no driftwocd. The inlets are too small to carry drift, and 
the edge is too swampy to permit forest vegetation close enough to the 
water to have fallen timber in the water. 
This is locally known ag Mud lake. It figures on most of the 
maps as Rost lake, improperly spelled Ross. The name was given be- 
cause of the early residence at the lake of a Swede named Rost. 
The lake is apparently of glacial origin. In a short time it will be 
filled up. The grassy meadows in the immediate vicinity, all of them 
wet and swampy, are no doubt smaller lakes or portions of this lake that 
have been filled up by sediment and hydrophytic vegetation. 
As was stated, the animal and vegetable life is quite var- 
ied. Clustered about the dead stumps of the rushes were large masses 
of a fresh water sponge, Spongilla, green in color, with long fingerlike 
arms waving in the water. Very few shells were found. In the creek 
below the outlet a few young Margaritana margaritifera were taken. <A 
single dead Physa heterostropha was picked up in the mud bottom, while 
a few Pyramidula strigosa var. Cooperi were found in the adjacent woods. 
In Odonata the lake showed greater numbers and abundance than 
any similar region studied in the state. Many species were just emerg- 
ing from the water. A Calopteryx, the first seen in the state and the 
first reported, was found rather abundantly. Sympetrum rubincundula 
was emerging, July 14, in large numbers, the specimens being fresh and 
uncolored. Aeschna constricta was on the wing, the exuviae being found 
on the rushes in numbers. Ischnura was common. Libellula pulchella 
was just emerging, in considerable numbers. Libellula quadrimaculata 
was on the wing, and captured specimens showed that they had been out 
for some time. Two species of Lestes were on the wing in considerable 
numbers, the larger number just emerging. A dark colored Sympetrum 
was sparingly distributed, difficult to catch, a single one being taken. 
Enallagma calverti Morse, was quite abundant, some on the wing, others 
emerging. A Mesothemis, M. simplicicollis, was occasionally seen, and 
one was captured on the mountain eastward at an altitude of over 7,000 
feet. 
Calopteryx yakima Hag. See Psyche, 1889, pp. 248-9. 
Hagen described this species from specimens collected at Lone Tree, 
near the Yakima river, Wash. He says the discovery of a species of 
Calopteryx west of the Rocky mountains was very unexpected and rather 
