Juday—Studies on Some Mountain Lakes. 791 
snow-clad mountains. Affluents are numerous, especially dur¬ 
ing the early part of the summer when the snow is melting 
rapidly. The largest of the affluents is the Upper Truckee 
river. The outlet of the lake is known as the Truckee river. 
Ko attempt was made to get temperatures in the deeper 
water. On June 27, 1904, the temperature of the surface 
water was 16° C. and of the bottom water where the depth 
was only 130 meters, 4.9°. In September 1873, LeConte 
found the temperature of the surfa.ee water to be 19.4° and of 
the bottom water at a depth of 460 meters 4°. The winters 
in this region are usually pretty severe, so that the air prob¬ 
ably remains far below the freezing point for a considerable 
period each year. Uotwithstanding this fact, however, ice 
never forms on the lake except in the shallow bays. 
The water is very transparent. A S'ecchi’s disk just dis¬ 
appeared from view at a depth of 20 meters. Later in the 
season, however, when the greater portion of the snow has dis¬ 
appeared and the affluents are no longer bringing vast quan¬ 
tities of roily water into the lake, the transparency is said to 
he much greater, white objects being easily seen at a depth of 
more than 30 meters. 
The larger, shallow-water forms of aquatic plants were 
found to be comparatively scarce. In the more favorable lo¬ 
calities such forms as Scirpus, Batrackium, Potamogeton and 
Carex were noted. Diatoms constituted the chief portion of 
the phytoplankton. 
ZOOPLANKTON FORMS. 
Copepods made up at least three-quarters of the bulk of the 
plankton. The limnetic members of this group' were Epi- 
schura nevadensis and a species of Diaptomus. The following 
Cladocera were noted:— 
Daphnia pulex pulicaria Uorbes. 
Daphnia hyalina rickardi Burckhardt. 
Simocepkalus serrulatus Koch. • 
Ilyocryptus acutifrons Sars. 
Eurycercus. lamellatus O. F. Muller. 
Acroperus karpae Baird. 
