AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 
221 
larger body of warm water than either of the others. It drains, according to the 
published map of the Geological Survey, a larger basin in proportion to its size and 
is bordered on the north by a marshy tract 24 miles long by nearly a mile wide. Its 
surface lies 250 feet below that of Lewis Lake and 270 below the Yellowstone. Its 
waters are very clear, but are nevertheless much more weedy alongshore than those 
of either of the other lakes. 
The slope of Mount Sheridan continues downwards into the lake a little distance, 
and the water consequently deepens rapidly from the eastern shore. About 200 feet 
out the depth was 91 feet; at 400 feet it was 124; and at 1,000 feet it was 146. The 
bottom temperature at this latter depth was 40° F. 
Our camp was pitched on the western side, about half a mile from the mouth of 
Witch Creek, and our work was confined to this shore and to a distance of about half 
a mile along the northern shore. Our dredgings here were made in three localities: 
in shallow water inshore, at a depth of about 10 feet; upon rocks a little distance out, 
at a depth of 30 feet; and in deep water from 46 to 120 feet, with a bottom of soft mud. 
Collections were made with the surface net from the open water at various hours of 
the day from 9 a. m. to 9 p. m., under such conditions of weather as offered themselves, 
and also from shallow water among weeds, commonly near the bottom. In addition 
to these, considerable collections of fishes were made with the trammel net and the 
smaller seines, the latter of which we used in Witch Creek as well as alongshore in 
the lake itself, and from these fishes a quantity of material was obtained for a study of 
the food of the various kinds. 
As might be supposed, some noticeable differences appear on a comparison of our 
collection lists, some readily accounted for and others at present inexplicable unless 
as the secondary or more remote effects of the first. It is naturally to be expected 
that in so small a lake, and one with so few opportunities for successful concealment 
or escape, the kinds of invertebrates on which fishes feed by preference would be 
unable to maintain themselves in as large numbers as in similar situations where 
fishes do not occur at all; and especially will this necessarily be true if we find that 
the fishes destroying these invertebrates are not strictly dependent on them for food, 
but eat other things as wel 1 . This is true of both the trout and the sucker, the former 
being almost indiscriminately carnivorous, and the latter mixing insect larvae and the 
like with a large proportion of vegetable food. 
It is probably in this way that we are to explain the fact that we did not find in 
our stay on this lake a single larva of Neuronia (the largest caseworm in these waters), 
so abundant in Shoshone Lake, nor a single amphipod crustacean ( Gammarus or 
Allorchestes) — all large enough to afford an attractive food to one or all of the fishes in 
these waters. That they occur here I can scarcely doubt, although the distribution 
of the Gammarus seems at best very whimsical in this region, but they certainly were 
far less common than in the adjacent lakes. The absence of the larger leeches (Nepli- 
elis maculatus) may be due to our failure to find suitable places for them, or they also 
may be eaten by fishes. 
More difficult to understand is the very remarkable fact that we did not find here 
so much as a single specimen of the almost gigantic copepod, Diaptomus shoshone , 
although its companion elsewhere, the smaller species of Diaptomus , was extremely 
abundant in all our open-water hauls. Equally difficult of explanation was the vast 
abundance of the entomostracan Daplmella bracliyura — not once taken before we 
