64 Conservation Department 



ber 12. Asterionelhi and Frayildria g-radually increased through 

 the season until on September 12 at station 05 the former reached 

 1575 per liter and the latter 1610 per liter. Stepluuiodiscus and 

 Melosira were about equal in numbers, both occurring to a lesser 

 degree than did the other three important genera of diatoms. 

 Gyrosigma, SurireUa and Cijmafopletira were infrecpiently found 

 in small number. The centrifuge recovered considerable quanti- 

 ties of Synedra throughout the summer as well as minor amounts 

 of Navicida, Nifzschia and Cocconek. The relatively small num- 

 ber of nannoplankton species in the lake Avas very noticeable 

 tliroughout the summer. 



Dinophyceae. Ceratium hirundineUa Avas important during the 

 entire season and shoAved a gradual increase in September. Peri- 

 dinium Avas very rare in occurrence. 



Eugleninae. A fcAV specimens of EiKjlena Avere taken in the 

 middle of August, but this genus Avas not found in the plankton 

 at ?i\\y other time. 



JMyxophyceae. Nine genera represented this group of algae. 

 Of these Anahaena AA^as abundant in early summer falling doAvn 

 considerably in August but increasing again in September. In 

 late August and September Aphanoihece made itself knoAvn in fair 

 quantity Avhere it had occurred only as scattered traces in July. 

 Aphanizomenon was found in abundance at several stations in 

 early July but during August and September it had all but disap- 

 peared. Small quantities of Nostoc appeared in September. Dur- 

 ing August Microcystis flourished in a moderate Avay, occurring 

 abundantly in the foot net toAvs at stations 05 and 23 aiid not at all 

 at stations 01, 02, 7A, 09. Coelospliaerium, Lynybya and Aphano- 

 capsa Avere irregular and sparse in occurrence. 



Protozoa. Vorticella Avas the chief member of this group, occur- 

 ring in large quantities attached to Anahaena colonies. In Sep- 

 tember there Avas a decline. Diffiugia and Amoeba occasionallj^ 

 appeared in small amounts. An unidentified Helizoan occurred in 

 both the net and centrifuge collections more abundantly during 

 August than at any other time. 



Rotifera. Polyarthra Avas most frequently found. It Avas grad- 

 uall}^ on the increase at the end of the season. During July 

 Anuraea cochlearis Avas rather fre(|uent but in September none 

 was found. Conochilus unicornis Avas very common at several 

 shallow water stations in early July. It Avas never again found 

 commonly. Ploesonia, Trochosphaera, Asplanchna, Anapus and 

 Asplanclinopus were taken in shalloAv Avater early in JuIa' but not 

 later in any of the deeper stations. 



The Quantity of Microplankton. — In order to adequately 

 present the data from the s1an(l|)()int of disti-ibution, both verti- 

 cally and hoi-izontally, and to show the effects of seasonal A^aria- 

 tion Avould re(iuire more s])ace than can be allotted to this discus- 

 sion. Hence a brief presentation of the (piantitative data Avill be 

 given here, leaving certain additional features for the nun-e com- 

 plete treatise to be published elsewliere. 



