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 2 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 94 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. in. 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 well. 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 (Oammarm 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 (Neph- 

 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 Diaptomm, was extremely 

 abundant in all our open-water hauls. Equally difficult of explanation was the vast 

 abundance of the entomostracan Daphnella brachyura not once taken before we 



