THE IJFK OF DKA'IlvS I.AKK 81 



PLAN ARIA 



But a single species of this group (Gyratrix hermaphroditus) 

 has been found in the Devils Lake complex, an occasional specimen 

 being taken in collections from Ruppia in the main lake. 



XEI\IATODA 



The nematodes of the complex are numerous in individuals 

 and undoubtedly in species, but as yet complete identifications are 

 not available. Dr. N. A. Cobb of the U. S. Department of Agri- 

 culture has kindly given me the following list, based on fresh mate- 

 rial which reached him, for the most part, in poor condition. 



Monohystera sp. "Very commou." 



Monohystera sp. "Not common." 



Diplogaster sp. "Common." 



Achromadora sp. "Rare." 



Ironus sp. "Not common." 



Plectus sp. "Not common." 



Dorylaimus sp. "Rare." 



Dorylaimus sp. "Rare." 



Cephalobus sp. 



Chromadora americaiia n. sp. "Rather common." 



The nematodes occur mainl}^ in the Ruppia zone and in the 

 ooze, but are occasionally present in the plancton catches. They 

 occur at all seasons of the year, both in winter and summer, but 

 no attempt has been made to determine their relative abundance 

 at different times. 



ROTIFERA 



Both in respect to numbers and variety the rotifers are the 

 most important animals in the Devils Lake plancton. Thirty-one 

 species and one sub-species occur, two of them, Brachionus satanicus 

 and Pedalia fennica, at certain times in great numbers. 



The attached forms naturally are found in the Ruppia zone, 

 which also shelters a number of the rarer, free swimming forms. 

 All of the latter are probably of widespread distribution thruout 

 the lake, but the rarer forms occur so infrequently that but little 

 can be said regarding their distribution, either spatial or temporal. 



Reproduction is almost entirely parthenogenetic, males of any 

 species having been seen in very few instances. The difficulty of 

 recognizing males in preserved material may, however, partly 

 account for this. 



The seasonal distribution of the rotifers as a whole is shown 

 ii) pi. 17 and figure 22, anent which the same remarks apply as 

 those made anent that of the Crustacea.* The distribution of those 

 species which occur in the collections in numbers large enough to 



♦See p. 87. 



