57 



THE ROTIFERA OF DEVILS LAKE, WITH DESCRIP- 

 TION OF A NEW BRACHIONUS. 



By Charles F. Rousselet, F.R.M.S. 



{Read January 2%th, 1913,) 



Plates 5 and 6. 



Devils Lake, the largest body of water in North Dakota, U.S.A., 

 is approximately 30 miles long by 5| miles wide at its broadest 

 part, and of very irregular shape. It receives its water from 

 a territory which forms an inland drainage basin extending 

 northwards as far as the Turtle Mountains. 



From the records it appears that the level of the lake has 

 fallen 14 feet since 1883 (when it stood at 1,439 feet above sea- 

 level) and 16 feet between 1830 and 1883, making a total 

 recession of 30 feet in eighty years with a corresponding shrink- 

 age of the area of the lake. At the time of its highest level the 

 lake had an overflow outlet at its eastern end into Stump Lake 

 lying further east, and it is probable that this high-water level 

 was reached many times in past centuries through periods of 

 scanty rainfall succeeded by periods of unusually abundant pre- 

 cipitation. In 1910 the level of the water stood at 1,425 feet 

 above sea-level, but fluctuates about 4 feet between very dry 

 and wet periods. The lake has had no outlet for a long period, 

 and as the result of evaporation the water has become brackish, 

 the salinity increasing gradually by concentration, until at the 

 present time the water has a specific gravity of 1*0076 (the 

 sp. gr. of sea water being 1*027). 



Besides common salt the water contains appreciable quantities 

 of sodium sulphate and magnesium sulphate, carbonate and 

 bicarbonate, so that it is alkaline as well as brackish, and this 

 no doubt accounts for the very peculiar and remarkable Rotif erous 



