297 



Rot if era: 



Brachionus dorcas, female 1 



Rotifer tardus, female 9 



Polyarthra platyptera, female 2 



Polyarthra platyptera, female with 



1 egg 1 



Indeterminate rotifer sp 1 



Entomostraca: 



Cyclops bicuspidatus, female, young, 



dead or moribund 1 



Cyclops, young 2 



Cyclops, nauplii 4 



Canthocamptus, nauplii 4 



Chydorus globosus 1 



Miscellaneous: 



Rhabdocoel 1 



Dero vaga 2 



Indeterminate 7 



Total 43 



In towings made at the time of the quantitative collec- 

 tions Mr. Hempel found an individual each of Pterodina patina 

 and Notholca acuminata. 



The list includes representatives of the prominent winter 

 planktonts excluding algse and diatoms. The effect of the 

 sewage contamination is observed in the reduced numbers 

 both of individuals and species, in the moribund condition of 

 Difflugia, Carchesium, Epistylis, Brachionus, and Cyclops, and 

 in the fact that apparently the only breeding forms, with the 

 exception of the Cyclops, were the ubiquitous and perennial 

 Polyarthra and the muck-loving Canthocamptus, and possibly 

 the slime-dwelling Rotifer tardus. 



This incident affords a striking illustration of the catas- 

 trophic effect of the ice blockade upon the life of sewage-fed 

 streams in whose waters the products of decay are concen- 

 trated by the exclusion of the air by the ice sheet. 



The absence of collections in March prevents any tracing 



