AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 
227 
As we worked into shallower water the Gammari and the leeches became more 
abundant, especially Clepsine , and at 25 to 50 feet univalve mollusks ( Planorbis exacutus 
and Physa), Allorchestes 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 , Conochilus , all abundant, many oligo- 
cliaete worms, leeches and leech capsules, Physce, Limncece , Allorchestes , Gammari , 
and cyprids ( Cypris barbatus , n. sp.), various case worms, nymphs of Ephemeridce , 
Chironomus larvae, and larvae of Tabanidce 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 yonng 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 Creek, 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 and insect larvae. Amphipod crustaceans were very scarce in 
this creek, Gammarus not occurring in our collections, and Allorchestes but once; and 
among eutomostraea, 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 algae 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 and of Cypris, and a single Allorchestes. Among 
the algae, besides the foregoing, several examples of Simoceplialus vetulus were taken, 
together with Bosmina, Ceriodaphnia , Polyphemus , and Chydorus sphcericus. The most 
abundant insects were, of course, Chironomi — larvae, pupae, and adults just emerging — 
and ephemerid larvae. A few Corisce and caseworms, some small aquatic Coleoptera, 
and a single living Limncca were also noticed. 
In the shallower and swifter parts of the stream insect larvae 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 Chironomus, ephemerid and perlid larvae, 
large Corisce, 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 larvae 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 
