297 
Rotifera: 
' Brachionus dorcas, female......... 1 
Rotifer tardus, female............. 9 
Polyarthra platyptera, female...... 2 
Polyarthra platyptera, female with 
ec ea ae ee Oe 1 
Indeterminate rotifer sp........... 1 
Entomostraca: 3 
Cyclops bicuspidatus, female, young, 
dead or moribund..... 1 
Cyclops, yOUne g. < <c2 002300522 2 
Cyclops, Gaps Lae sho eee sks s 4 
Canthocamptus, nauplii..........-. 4 
Chydorus globosus..........50+.-+s 1 
Miscellaneous: 
NRA DONEUEE a5 oe is aes he eines ss 1 
DRG AGW S irate cnie ome sed Ss oa a 2 
Indeterminate 2... 7.202 <2 268.6% ra al 
Tiga oes mee o-ale oa 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 alge 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 
