131 



waters, and of these parasitic forms will reveal the great richness of 

 the ciliate fauna in this aquatic environment. 



SUCTORIA. 



Average number, 332. This class is not quantitatively im- 

 portant in the plankton, being represented, in so far as our records 

 go, only by adventitious or passive planktonts. No limnetic species 

 has as yet been found in the Illinois. An examination of the 

 littoral region during the prevalence of ciliates wilt probably yield 

 a rich suctorian fauna. 



DISCUSSION OF SPECIES OF SUCTORIA. 



Acineta linguifera Clap, and Lach. This species is usually found 

 on aquatic Coleoptera. A single occurrence of an unattached indi- 

 vidual was recorded June 21, 1898. 



Metacineta mystacina Ehrbg. Average number, 301. This 

 species occurred in the plankton from March till October in 1898 and 

 in the winter months of 1899, at irregular intervals and in small 

 numbers (Table I.). Most of its occurrences attend flood invasions, 

 and it is evidently adventitious. It is frequently attached in the 

 plankton to minute particles of debris. This species varies greatly 

 in the size of the lorica. Sand ('01) gives the range in height as 

 from 3 3-7 00 -/i. The variation in proportions has given rise to a 

 number of descriptions of new species by Stokes ('88 and '94) and 

 Maskell ('87), but an examination of a series of individuals such as 

 appear in the plankton shows that they intergrade so closely that 

 specific distinctions can not be maintained for the variants. Meta- 

 cineta appears throughout the whole range of temperatures, no 

 seasonal predominance appearing in the records. 



Podophrya fixa O. F. Mull. Average number, 12. This species 

 is also adventitious in the plankton. It was recorded in March and 

 September at 37 and 73. Cysts were noted January 21. 



Tokophrya quadripartite Clap, and Lach. Average number, 4. 

 Adventitious in the plankton in March and November. Hempel 

 ('99) finds it most abundant in May and June, associated with 

 Epistylis plicatilis and Opercularia irritabilis on crayfish, insect 

 larvae, and turtles. 



Tokophrya cydopum Clap, and Lach. Found occasionally upon 

 Cyclops during spring and summer. 



(10) 



