240 Wisconsin Academy of Sciences, Arts, and Letters. 
and ‘Cayuga shows that the number was somewhat greater in 
the upper water of the latter, but the former possessed a greater 
variety of forms. The copepods were represented only by the 
genus Cyclops in lake Atitlan, but by both Cyclops and Diap- 
tomus in Cayuga. The number of copepods was very much 
greater in Atitlan than in Cayuga. 
There was a very marked difference in the rotifer population 
of these two lakes, Cayuga having a much larger number as well 
as a greater variety. The protozoa were not represented in the 
catches from Atitlan but these forms constituted a very import¬ 
ant element bf the plankton of Cayuga. 
The total number of algae was much greater in Atitlan but this 
superiority in numbers was due to the presence of only one 
species, namely, Melosira granulata. 
When lakes Atitlan and Seneca are compared the results are 
still more favorable to the former. It possessed a larger number 
and variety of cladocera and a distinctly larger number of cope¬ 
pods. The rotifer population of the two lakes did not differ so 
greatly in number but there was a distinctly greater variety in 
Seneca lake. The protozoan population was comparatively small 
in Seneca and absent in Atitlan. The total number of algae was 
very much smaller in Seneca lake but it possessed a greater var¬ 
iety of forms. 
Lake Ilopango possessed a very much smaller number of clad¬ 
ocera than either Cayuga or Seneca lakes and the copepoda were 
represented only by Diaptomus siciloides and its nauplii. In 
lake Ilopango the rotifers belonged to but three genera while 
in Cayuga and Seneca at least nine genera were present. In 
point of number of individuals Ilopango far outranked the tem¬ 
perate lakes owing to the presence of such large numbers of 
Pedalion fennicum, a brackish water rotifer. 
The protozoan population of Ilopango greatly exceeded in 
number that of Seneca lake, but was smaller than that of 
Cayuga. In Ilopango the algae were represented only by a few 
diatoms, while the net catches from Seneca lake contained a few 
blue-greens and a fair number of diatoms; those of Cayuga lake 
also contained a relatively small number of blue-green algae, 
but a fairly large number of diatoms. 
The cladoceran population of lake Coatepeque consisted of two 
forms, Daphnia hyalina and Ceriodaphnia pulchella. The cope¬ 
pods were represented only by Diaptomus sicilis whose numbers 
