AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 229 



Physa (small ami large, ia quantity), Pisidium, many Limncea;, of various sizes, Planor- 

 bis, and small Amniuolce, accounted sufficiently for the fry of the mountain trout 

 abundant among the woods. The mast interesting object here, however, was a small 

 cylindrical brown turbellarian, which lias the habit of swimming freely through the 

 water, rolling over steadily from side to side as it swims, Although common here and 

 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, Pereuyi'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 nearly 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 alga; 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 

 (jammarus robwtita and of Allorchentes inermis, caseworms with cases made of fragments 

 of bark, larv;e 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 GonoeMIus 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 Polyphemux as of all other ento- 

 mostraca. The Diaptomi were D. shoshone (a few) and several I), nicilis, and all the 

 other cntomostraca were a few each of Cyclops xerrulatus, Saapholcberis mucronntus, 

 and Chydorun xphtcricm. 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, witli a temperature of 103 F., containing much Ottdllaria and 

 full of a dark-red alga, there were many holotrichous infusoria and other smaller ciliata, 

 minute flagellata, a fine anguillnlid, a small, active planarian, and many examples of a 

 rotifer (Monostyla) allied to M. cormtta, but apparently new. (See page 250.) 



