352 Illinois State Laboratory of Natural History. 



the year, the species of Rot if era, on the other hand, often 

 have a well-marked period of abundance, with scattering 

 occurrences at other times. The season of abundance varies 

 greatly even in species of the same genus. Some are summer 

 and some winter species ; some have shorter and some longer 

 periods. In general the group is well represented throughout 

 the entire year. No towing was taken by us at any time that 

 did not contain some rotifers. In 1894 they were most 

 abundant from June to September, while comparatively few 

 species were listed in October. The December records show 

 an increase in such forms as Brachionus, Anuraa, and 

 Notholca. On February 23, 1895, towings were taken at 

 substation G, under eighteen inches of ice, which were re- 

 markable for the abundance of life they contained. Eight 

 species of rotifers were found in this catch, three of which 

 included individuals with eggs attached. 



The forms which were common enough to show definite 

 indications of their seasonal distribution are given in the fol- 

 lowing list, which can be greatly improved — perhaps in some 

 cases disproved — by more extensive and systematic observa- 

 tions. The period of greatest abundance is given in italics. 



Floscularia ornata : Sept. 



Megalotrocha semibullata : July, Aug. 



Conochilus : Jan., Feb -July, Aug., Sept. 



Rotifer: July-Sept., Oct.-June. 



Philodina : June-Sept., Oct. 



Asplanchnidse : Jan., Feb., Apr.-Sept., Nov., Dec. 



Synchaeta pectinata : Sept.-May, June, Aug. 



S. stylata : July-Sept., Oct. 



Polyarthra platyptera : Dec-Mar., Apr.-Nov. 



Triarthra longiseta : Feb., Apr.-Sept., Dec. 



Ploesoma lynceus : May, June, July-Oct., Nov., Dec. 



Notommatida; : June, July-Sept., Oct. 



Mastigocerca bicristata : May, June-Sept., Oct. 



Coelopus : June-Aug. 



Dinocharis pocillum : Mar.-July, Oct.-Jan. 



Salpina eustala : June, July-Sept., Oct. 



Euchlanis : Apr.-June, July-Sept., Oct. -Dec. 



