578 The American Naturalist. [July, 
Occasionally found in large numbers. Bursaria, Chloromonas, 
Glenodinium, Mallomonas, Raphidomonas. 
Commonly found in small numbers. Anthophysa, Ceratium, 
Cercomonas, Codonella, Epistylis, Monas, Tintinnus, Trachelo- 
monas, Vorticella. 
Occasionally observed. Acineta, Chlamydomonas, Coleps, 
Colpidium, Euchelys, Euglena, Euplotes, Glaucoma, Halteria, 
Heteronema, Nassula, Paramaecium, Phacus, Pleuronema, 
Raphidodendron, Stentor, Synerypta, Trichodina, Uvella, 
Zoothamnium. 
ROTIFERA. 
Commonly found in small numbers. Anuraea, Conochilus, 
Polyarthra, Rotifera, Synchaeta. 
Occasionally observed. Asplanchna, Colurus, Eosphora, Flos- 
cularia, Lacinularia, Mastigocerca, Microcodon, Monocerca, 
Monostyla, Noteus, Sacculus, Triarthra. 
CRUSTACEA, 
Commonly found in small numbers. Bosmina, Cyclops, 
Daphnia. 
Occasionally observed. Alona, Cypris, Diaptomus, Sida. 
MISCELLANEOUS. 
Occasionally observed. Acarina, Anguillula, Batrachosper- 
mum, Chaetonotus, Gordius, Hydra, Macrobrotus, Meyenia, 
Nais, Spongilla ; besides spores, ova, insect scales, pollen grains, 
vegetable fibres and tissue, yeast cells, starch grains, ete. 
An examination of the following table, a numerical sum- 
mary of the preceding list, brings out some interesting facts :— 
It will be observed that 186 genera have been reported, 108 
plants and 78 animals. Of these only 18 are commonly found 
in large numbers, 13 plants and 5 animals. Twenty-one more 
are occasionally found in large numbers, 16 plants and 5 ani- 
mals. Forty-one genera are frequently seen in small numbers, 
while 106 genera, or more than one-half of all are seen occa- 
sionally, some of them but rarely. The most important classes 
are the Diatomacee, Chlorophycee, Cyanophycex and Infu- 
soria, as shown by the large number of genera and by their 
greater abundance. Furthermore, these classes include all but 
one of the 23 troublesome genera that have been found in large 
numbers. Eleven genera may be said to be very troublesome, 
because of their wide distribution, the frequency of their occur- 
