238 ^Wisconsin Academy of Sciences, Arts, and Letters. 
In one of the bottom hauls two specimens of Hyalella dentata 
were obtained. 
Lake Ilopango.—The net plankton of lake Ilopango was char¬ 
acterized by the scarcity of the phytoplankton. Relatively 
small numbers of Cyclotella and Synedra were obtained in the 
upper 25 m. Zygnema was the only other alga noted in the 
catches. A few specimens of it were found in the upper 10 m. 
The protozoa were represented by a few specimens of Dino- 
bryon in the upper 10 m. and by a considerable number of 
Tintinnus. The latter was found throughout the depth of the 
lake, but was most numerous in the 10-25 m. stratum. 
Pedalion fennicum was the only rotifer obtained throughout 
the depth of the lake. It was very abundant in the upper 10 
m. Anuraea stipitata and Notlnolca longispina were found only 
in the 25-50 m. catch. 
The only copepod noted was Diaptomus siciloides which was 
present at all depths, but was most abundant between 10 m. and 
25 m. Nauplii were present in small numbers at all depths. 
Only one cladoceran was noted. A few specimens of Ceri- 
odaphnia pidchella were found between 10 m. and 50 m. 
Coatepeque lake.—-The net plankton of this lake was also poor 
in phytoplankton, but it was not as poor as that of lake Ilopango. 
Here, too, a diatom, Cyclotella , was the most abundant form. 
It was scarce in the upper 25 m., but was distinctly more plenti¬ 
ful below this depth, the maximum number being found in the 
bottom stratum. This distribution seems to indicate that this 
form was on the decline. 
The blue-green algae were represented by a small number of 
Clathrocystis in the upper 25 m. and by a still smaller num¬ 
ber of Aphanizomenon in the upper 10 m. 
Ceratium and Tintinnus were the protozoan representatives. 
The former was present in relatively small numbers throughout 
the depth of the lake. The latter was much more abundant, 
with the maximum number in the upper 25 m. 
The rotifers were represented by a contracted Bdelloid form, 
probably belonging to the genus Rotifer , and by Pedalion fenni¬ 
cum. The former was abundant in the upper 25 m. and a very 
few of the latter were found in this stratum. 
The copepods were represented only by Diaptomus sicilis 
which was found at all depths, but which was most abundant in 
the upper 10 m. A small number of nauplii was noted from 
surface to bottom. 
