58 C. F. ROUSSELET ON THE ROTIFERA OF DEVILS LAKE 



fauna it contains, which is abundant in numbers but very re- 

 stricted in species. 



Since 1910 a Biological station has been established on the 

 shores of the lake by the Legislative Assembly of the State of 

 North Dakota, under the control of the Biological Staff of the 

 State University. 



At the request of Prof. R. T. Young I have at various times 

 examined samples of plankton collected by him in July 1910 and 

 May 1912, and have found therein only the following seven 

 species of Rotifera, the majority of them rare, strange and 

 unusual forms : 



Triarthra longiseta Ehrenberg (a single specimen, possibly 



accidental). 

 Pedalion fennicum Levander. {Very abundant.) 

 Asplanchna Silvestrii Daday. (Very abundant.) 

 Brachionus Midleri Ehrenberg. (Few.) 

 Brachionus satanicus Rousselet. (Very abundant.) 

 Brachionus spatiosus Rousselet. (Very abundant.) 

 Brachionus pterodinoides sp. nov. (Few.) 



Two of these forms I have already described as new,* and 

 have now to introduce a third still stranger species. 



The single specimen of Triarthra may have been introduced by 

 accident in one of the tubes. 



Rotifera are essentially freshwater animals, and brackish or 

 salt water does not suit the great majority of species; this ex- 

 plains the paucity of species living in Devils Lake. 



This fact does not militate against the theory of cosmopolitan 

 distribution of the class, on the contrary it confirms it, for 

 Pedalion fennicum is known from brackish lakes only in Finland, 

 Egypt, Central Asia, Asia Minor, etc. The presence in the lake 

 of the rare Asplanchna Silvestrii suggests that the " Lago di 

 Villa Rica," in Chile, from which it was first obtained, is a 

 brackish lake. Perhaps Prof. Silvestri, who obtained Daday's 



* Journ. Q.M.C., Ser. 2, Vol. XL, pp. 162 and 373 (April 1911 and 1912). 



