Ergasilus — Nauplii. 
333 
Ergasilus depressus Sars. 
This animal is about the same size as Cyclops, although 
readily distinguishable both by color and form. I am not sure of 
the correctness of the specific identification, although lean see no 
differences between my specimens and Sars’ description. It is 
present at all seasons of the year, ordinarily in very small num¬ 
bers. More than one individual is rarely found when one-tenth 
to one-twentieth of the catch is counted. This number is so small 
and the resulting probable error in computing averages so great 
that it has not been thought profitable to state the numbers in 
terms of a square meter of surface, and to include them in the 
total number of limnetic Crustacea. 
Ergasilus is present throughout the year, although it may 
often be missed for long periods from the collections. It was 
first noticed in July, 1895, although doubtless present before, 
and from 1 to 9 specimens were seen in each collection. The 
number increased during the latter part of August and in Sep¬ 
tember, when from 10 to 13 specimens were found, indicatiug 
nearly 10,000 per sq. m. In the latter part of September the 
numbers rose to a maximum of 27-30 specimens, or nearly 27, 000 
per sq. m. In October only 1 to 5 were present, and the species 
was found occasionally during the winter and spring in single 
specimens. In July and August, 1898, it became more plentiful; 
about as is 1895. But no such large number was found in Sep¬ 
tember as in the former year. The animal seems to prefer the 
stratum of water just above the thermocline, but is not confined 
to this layer. 
Copepod Larvae —Nauplii. 
The dredge with which my study was carried on until the 
middle of July, 1896, was provided with a bucket whose open¬ 
ings were closed by a wire mesh of 1-100 in. This, while re¬ 
taining the Crustacea and a great part of the nauplii, did not 
retain all of the latter, so that no study was given to these 
larval forms until work began with the silk net. The following 
table shows the average number of larvae from the middle of 
July to the end of December, and also the numbers found in 
