225] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 31 



not to be found in any of the masses of Spirogyra taken only a few feet away. 

 The coarser leaves of the Chara evidently harbored more protozoa, and more 

 organic debris thus furnishing a larger supply of food, but the oxygen in that 

 region must have been very much less. No specimens were taken at the sur- 

 face. They were always down a few inches where the water was quite cool. 

 Stenostoma leucops was present in only small numbers and Stenostoma giganteum 

 was very numerous. The food seemed to be almost entirely protozoa and 

 small Crustacea, the size of the worm making it possible for it to swallow 

 easily individuals of different species. 



The movements were invariably slow and the twistings and turnings so 

 characteristic of Stenostoma leucops were very nearly lacking. Most of the 

 specimens were made up of two zooids, and not a single chain of more than that 

 was found. They were negatively heliotropic. Their length of life has not 

 been ascertained, as they were found only during the summer months. A num- 

 ber of collections were made during January, under eighteen inches of ice 

 but the very shallow water below this thickness showed only a very few Crus- 

 tacea. Dead fish were seen and it was apparent that very little oxygen 

 was left in this bottom layer. 



The relations with other forms seemed quite simple. The only enemy 

 of this Stenostoma was probably the fish, and the whole life condition was 

 without great struggle. 



Among the other animal types to be seen in the collections, this species 

 was very conspicuous, even to the naked eye. It was the largest of the nearly 

 microscopic forms and moved quite enough to be easily distinguished. As 

 has been mentioned, ninety percent of the specimens were composed of two 

 zooids, and such individuals averaged in length from one to two miUimeters. 

 The two parts v/ere not quite equal, the anterior generally being a little the 

 longer, so that measurements would average about 0. 7 to 0.9 mm. for the posterior 

 segment and 0.8 to 1 mm. for the anterior segment. The single individuals were, 

 as a rule, those which had lately split and were of ordinary condition. They 

 were almost always a little over one millimeter, but never reached the length 

 of 2 mm. The width and depth were very nearly the same except in the 

 tail region and in the very anterior end. This diameter was from one-fifth 

 to one-quarter the entire length of a double individual or in many instances 

 where a separate segment was measured, was as much as one-third the length. 

 On the whole, this species seemed about twice as large as the common Steno- 

 stoma leucops. 



In shape, these specimens are quite different from other members of the 

 genus. They are not so slender, but seemed more stubby and rod-like. The 

 ratio of diameter to length is 1 to 4 or 5, rather than 1 to 7 or 10. Not so agile 

 or flexible, they seem stiff cylinders, tapering off bluntly to a short tip. That 

 is, from about the middle of the posterior zooid to a point just behind the 

 mouth, the diameter is always the same (except at the fission plane). The 

 region around the mouth is somewhat protruded as a sort of circular lip which 



