576 The American Naturalist. | [July 
BIOLOGICAL STUDIES IN MASSACHUSETTS. 
By GrorGe C. WHIPPLE. 
MICROSCOPICAL ORGANISMS. 
The examination of nearly forty thousand samples of water 
in Massachusetts collected from water supplies differing in 
locality and character, and extending through all seasons for 
a long term of years serve to give us a good idea of the micro- 
organisms inhabiting the fresh waters of this region. But, in 
studying them it must be remembered that the examinations 
were made from a sanitary standpoint, and that from the 
. manner in which the samples were collected they include only 
such forms as are found floating in the water: the littoral 
forms are not represented except as they have become de- 
tached and accidentally carried into circulation. 
The following table gives the names of the genera thus far 
observed. They are arranged according to the usual system 
of classification, and each class is divided into groups, accord- 
ing to abundance and frequency of occurrence. The first 
group includes those genera which, in their season, are often 
found in large numbers; the second group includes those 
which are only occasionally found in large numbers; the third 
those which often occur in small numbers; the fourth those 
which are rarely observed. This division, while not wholly 
satisfactory, enables us to separate the important from the un- 
important forms. As observations multiply, the list will doubt- 
less be extended and many genera will be changed from one 
group to another. The names printed in heavy type indicate 
that the organisms so marked have been the cause of trouble 
in a water supply. 
DIATOMACE&. 
Commonly found in large numbers. Asterionella, Cyclotella, 
Melosira, Synedra, Tabellaria. 
Occasionally found in large numbers. Diatoma, Fragilaria, 
Nitzschia, Stephanodiseus. 
Commonly found in small numbers. Epithemia, Gomphon- 
ema, Navicula, Stauroneis. ite 
