Bosmina loncirostris , Daphnia being the most important. 



The collections in the western end of Lake Erie show distinct 

 changes in the composition of the plankton during the course of the 

 year. The picture is incomplete because of the small numbprs of vjinter 

 collections. As far as can be ascertained from the present collections 

 the succession of forms is as follows; 



From January to March there is little change. The Crustacea 

 present during these three months are Diaptomus mi nut us , D. sicilis. 

 D. ashlandi, Cyclops bicuspidatus , and Limnocalanus macrurus . Diaptomus 

 forms the major part of the collections. Limnocalanus and Cyclops 

 bicuspidatus are present in immature forms. It is probable that more 

 complete collections would show the presence of larval Epischura, although 

 none of this species was found. 



In April the winter species persist and in addition Epischura, 

 Diaptomus oregonensis , Cyclops americanus , and the Cladocera Bosmina 

 longirosTris , and Daphnia pulex pulex . The Cladocera appear first in 

 enclosed areas and are abundant nowhere until May, Cyclops bicuspidatus , 

 which was present in small numbers and in larval form, becomes abundant. 



In May there are added to the species of April Cyclops 

 leuckarti in large numbers and the Cladocera Daphnia ( retrocurva ) and 

 Diaphanosoma leuchtenbergianum . Late April is a transition period and 

 in May the full summer fauna is established. 



During June, July, and August the fauna has the same composi- 

 tion as in May, the prominent species being Diaptomus oregonensis , Cyclops 

 leuckarti , Epischura lacustris and the Cladocera, especially Daphnia 

 (retroc"urvay^ Cyclops bicuspidatus becomes less abundant after June, 

 Diaptomus minutus is more abundant in summer than at other seasons. 

 Cyclops prasinus appears in August; this species has some significance, 

 but is never present in any considerable numbers. 



The September fauna is much like that of the summer months, but 

 Diaptomus sicilis and Diap^tomus ashlandi have disappeared. 



In October the only abundant cladoceran is Daphnia ( retrocurva ) ; 



Diaphanosoma leuchtenbergianum and Daphnia pulex pulex have disappeared, 

 and Leptodora kindtii is no longer prominent. Cyclops americanus has 

 disappeared, 



209 



