786 Wisconsin Academy of Sciences, Arts, and Letters. 
Simocephalus vetulus O. F. M. 
Geriodaphnia pulchella Sars. 
Eurycercus lamellatus 0. F. M. 
Gamptocercus rectirostris biserratus Schoedler. 
Pleuroxus procurvatus Birgo. 
Some plankton material was collected in a small lake on tli© 
side of Mount Elbert. This lakelet has an altitude of about 
3,000 meters. The Cladocera were represented by Daphnia 
pulex, Simocephalus vetulus , Pleuroxus procurvatus and GJiy- 
dorus sphaericus. 
Also some material was obtained from Willis lake, which is 
a tarn near the head of Willis gulch, a little southwest of Twin 
lakes. This lakelet is situated at an altitude of about 3,660 
meters. The water was very cold. Gammarus was plentiful, 
and the Cladocera were represented by two forms, Macrothrix 
hirsuticornis Norman and Brady and Eurycercus lamellatus 
O. F. M. * 
The plankton observations on the two lakes were few in 
number and consisted only of vertical hauls. In 1902, the 
observations on Upper lake consisted of two series of catches 
in July and four in August. A single set of catches was made 
on Lower lake in 1902. In 1903, three sets of catches were 
made on each lake. The observations covered such a brief 
period of time each year that they give only a very fragmen¬ 
tary notion of the plankton life of the lakes. Likewise, the 
vertical haul method is by no means a satisfactory one, so that 
both of these factors must be taken into consideration in the 
following results. The following table shows the number of 
thousands of individuals per square meter of surface. Hence, 
to determine the number of individuals per square meter, 
these figures must be multiplied by a thousand. With the ex¬ 
ception of a few figures for the rotifers, the numbers repre¬ 
sent averages of either two or three hauls. The rotifers were 
not counted in all the catches, so that, in a few instances, the 
numbers given for them represent the individuals of a single 
catch. 
