AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 229 
Physa (small aud large, in quantity), Pisidium , many Limnoew , of various sizes, Planor- 
bis, and small Amnicolce , accounted sufficiently for tlie fry of the mountain trout 
abundant among the weeds. The most interesting object here, however, was a small 
cylindrical brown turbellarian, which has the habit of swimming freely through the 
water, rolling over steadily from .side to side as it swims, Although common here aud 
easily taken, every effort at its preservation failed completely, the specimens going 
to pieces in spite of the varied use of hot water, corrosive sublimate, cold and hot^ 
osmic acid, Perenyi’s fluid, etc. This interesting form seems, notwithstanding, worthy 
of special mention, and I have drawn up the following brief description, made from 
field notes, which may serve to identify it to some collector more fortunate than I in 
his opportunity to study it closely. 
Form cylindrical, tapering a little toward both ends, the posterior end blunt- 
pointed, the anterior flattened in creeping, and broadly rounded. Locomotor surface 
not specially flattened. When swimming the two ends are similar. Length, when 
extended, 5 to 9 millimeters, width 1 millimeter. To the naked eye dark reddish or 
orange, slightly paler before and beneath. Closely examined, the color is in minute, 
irregular flecks on a yellowish ground, and varies in intensity, of course, according 
to the extension of the worm. Sometimes the intestine shows through as a darker 
median shade, and the orange-brown eggs, 0.25 millimeter in diameter, also deepen 
the color locally. When emptied of these, its color is nearly uniform reddish-brown. 
The eggs are spherical, conspicuous, in two ovaries, one each side of the abdomen, 
and, to the number of twenty, may neai’ly fill the body. A pair of eye-spots placed at 
a distance from the front of the head about equal to the diameter of the body. 
These worms were found in 1891 (September 1), much more abundant than at 
the above locality, in some clear, gravelly pools filled with filamentous algae along 
Soda Butte Creek. They were everywhere thick among the algae, and could be col- 
lected by scores in an hour. 
At the lower locality mentioned above, several ephemerid larvae, specimens of 
Gammarus robustus and of Allorchestes inermis, caseworms with cases made of fragments 
of bark, larvae of Simulium , and some small planarians were found. 
Finally I close this preliminary account of our Yellowstone Lake collections by 
noting the results of a brief examination of the contents of the warm waters along 
the shores of the hot-spring basin of West Bay. 
Hauling August 3, 1890, in shallow water only a few feet from shore, at tempera- 
tures varying from 70° to 101° F., where the ordinary surface temperature was 62°, 
we took a great quantity of the rotifer Gonochilus leptopus , very many examples of 
Polyphemus pediculus , a few Diaptomi , and a very few specimens of Daphnia pulex . 
There were probably five times as many examples of Polyphemus as of all other ento- 
mostraca. The Diaptomi were D. shoshone (a few) and several />. sicilis , and all the 
other entomostraca were a few each of Cyclops serrulatus , Scapholeberis mucronatus , 
and Chydorus splicericus. There were no insects in these collections, living or dead, 
and the total amount of animal life was much below that of the cold water adjacent. 
In a spring near shore, with a temperature of 103° F., containing much Oscillaria and 
full of a dark-red alga, there were many liolotrichous infusoria and other smaller ciliata, 
minute flagellata, a fine anguillulid, a small, active planarian, and many examples of a 
rotifer ( Monostyla ) allied to M. cornuta , but apparently new. (See page 250.) 
