240 
BULLETIN OF THE NATURAL HISTORY SOCIETY. 
ADDITIONAL NOTES ON DIATOMS. 
By L. W. Bailey, LL. D. 
In the preceding article reference has been made to the dia- 
tomaceous forms found in Plankton collections in and about 
Passamaquoddy Bay. A few words may be added as to the 
forms associated with the latter, their relative abundance and 
mode of treatment. 
These collections are made by means of plankton nets drawn 
through the water at some distance behind slowly moving motor 
boats. When allowed to stand the contents of the collecting 
bottles were found to settle very slowly, assuming at the surface 
of the deposit the appearance of a flocculent precipate, disturbed 
by the slightest movement. 
Examined in this condition, the collection is found to consist 
mainly of vast numbers of Copepods and related Crustaceans, 
mingled with great numbers of the Diatom Coscinodiscus, the 
whole forming a somewhat sticky mass, which soon begins to 
decompose, emitting a disagreeable odor. Reduced by evapor- 
ation nearly to dryness, and thoroughly washed, the residue is 
of a dark brown color, but still very soft and light. 
Examined in this condition, the Copepods, etc., will be found 
to have been largely or completely removed, the mass now con- 
sisting mainly of large Coscinodiscus (see preceding Plate I), the 
characteristic deep brown endochrome, which in the untreated 
frustules largely conceals their sculpture, having entirely disap- 
peared, while great numbers of marginal rings or hoops, derived 
from the same Diatom are seen. Coscinodiscus oculus-iridis is 
probably the most common form, but with this are specimens of 
C. radiatus and C. centralis. Another noticeable feature is the 
abundance of forms of the genius Chaetoceros, which, by its 
awns, often of extravagant length, are admirably adapted for 
flotation. There are many species, several of which are figured 
in the preceding plates. 
It is proposed to treat of all these forms more fully in a later 
article. 
