. AQUATIC INVERTEBRATE FAUNA OP WYOMING AND MONTANA. 227 



As we worked into shallower water the Gammari and the leeches became more 

 abundant, especially Glepsinc, and at '25 to 50 feet univalve in.ollu.sks (Planorbis exacutus 

 and Physa), Allorchestea inermis, small white Chironomi, larvae and pupae, and case- 

 worms in sand tubes appeared. At 15 and 20 feet, among the weeds, the assemblage 

 of associated animals was Daphnia, Diaptomus, Conoohilus, all abundant, many oligo- 

 chajte worms, leeches and leech capsules, Physa;, Limnaxe, Allorchextes, Gammari, 

 and cyprids (Cypris barbatus, n. sp.), various caseworms, nymphs of Ephcmeridce, 

 Chironomus larvae, and larvae of Tabanidte and Culicidce. 



No discussion, of the zoological resources and relations of Yellowstone Lake with 

 reference to fish-culture would be even approximately complete which ^did not take 

 account of the animal contents of the streams and other waters connected with it, 

 since these are the principal resorts of the young of the only species of fish the lake 

 now contains and must always be the chief breeding-places of fishes generally. 

 Apart from the river above and below the lake, the most important tributary is Peli- 

 can Greek, a peculiar stream for a mountain region in the fact that for 2 or 3 

 miles of its lower course it is broad, muddy, and comparatively sluggish, more like a 

 bayou than a creek, thick with vegetation, and much frequented by water birds, 

 whose feathers floating on its semi-stagnant surface gave it the appearance of a barn- 

 yard pond. Above this stretch, although still bordered by willow-covered and more 

 or less marshy bottoms, it becomes swift and rocky, except where cut across by 

 numerous beaver dams. 



The sluggish waters just above its mouth are, as might be expected, rich with 

 small crustaceans aud insect larvae. Amphipod crustaceans were very scarce in 

 this creek, Gammarus not occurring in our collections, and Allorchestes but once; and 

 among eutomostraca, gigantic specimens of Eurycercus lamellatus were far the most 

 numerous, making three-fourths of the entire bulk of the product of hauls made in 

 open water and among alg;e and other water weeds. With these, in open water, were 

 a new species of Macrothrix, a Diaptomus, an occasional Daphnia pulex, several speci- 

 mens of Cyclops, a few of Daphnella aud of Cypriit, and a single Allorchestes. Among 

 the algie, besides the foregoing, several examples of Simocephalus vetulus were taken, 

 together with Bosmina, Ceriodaphnia, Polyphemus, and Chydorus sphwricus. The most 

 abundant insects were, of course, Ghironomi larva}, pupae, and adults just emerging 

 and ephemerid larva}. A few Goriscc aud caseworms, some small aquatic Coleoptera, 

 and a single living Limncea were also noticed. 



In the shallower and swifter parts of the stream insect larva? take the lead, the 

 bulk of the collections consisting of large and small caseworms of various species, 

 most of them attached to stones, larvae of Ghironomux, ephemerid and perlid larvae, 

 large Gorisce, and several beetles of small size. The caseworms and ephemerid larvae 

 were exceptionally common. 



On the whole, this stream which must stand for the present as an example of 

 many others contained invertebrate forms of animal life in very fair abundance; in 

 the swifter waters the insect larvae (neuropterous and dipterous) which lurk under 

 stones, and in the more quiet parts entomostraca and insect larva- of different habit. 



A much smaller creek, known on the map as Bridge Creek, and noted among 

 tourists because crossed by a perfect and highly picturesque " natural bridge," has at its 



