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 driftwood. 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 as 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 sm^aller 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. Cooper! were found in the adjacent woods. 



In Odonata the lake showed greater numbers and abundance thark 

 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 



