288 Sketch of the Infusoria of the family Bacillaria 
The fluviatile species may be found in every pond, stream, 
rivulet, bog, or pool, either nestling among Conferve, parasitic on 
aquatic plants, or living in the sedimentary matter at the bottom. 
They often occur in such vast quantities as to cover hundreds of 
square yards, to which they give a peculiar color—green, yellow- 
ish or ferruginous, according to the peculiar internal coloring mat- 
ter of the individuals. Most of the species are exceedingly mi- 
nute, many are entirely invisible to the naked eye; others, how- 
ever, are quite perceptible without the aid of the microscope. 
Prise their extreme minuteness, it is evident, from 
their vast abundance, that they have some important offices to 
phot in the economy of nature ; and like the coral insect, al- 
though the individuals are saline, the result of their united la- 
bors is on a scale by no means insignificant. 
Few organic bodies exceed in beauty the symmetrical, ele- 
gantly sculptured forms of many of the species. ‘Their beauty, 
the singular phenomena they present, and the interest they have 
lately received from being detected in a fossil state in Europe and 
America, will be sufficient inducement for all lovers of micro- 
scopic research to study this family. 
“T shall now proceed to describe the most interesting American 
species, oe with the” = 5 
| DESMIDIACEA, 
Pree, carapace simple, nlite, ‘trilateral, often eatonate-— 
Mandl. and Ehrenberg, I. c. p. 244, 
1. Desmidium Schwartzii. Ag. (P\.1,fig.1.) “ Corpuscles smooth 
quadeagihliiron three sides, slightly emarginate, triangular on the other 
two sides, end obtuse, ovarium green, gly to ', of Paris line.” - 
The corpuscles of this species are united together by theit tri- 
angular faces, so as to produce long triangular (often twisted): fil- 
a armel: are of a beautiful green color, and 
_lubricous - Each filament. is enveloped in a very transparent 
ati inc Is ak which is not visible on the dead specimens: — 
filaments often occur together in great. quantities, and form a stra- 
tum in the water which is not. distinguishable frog age 
some species of Zygnema, with whi 
g@, this presents many points of resemblance. Allusion is ors 
