59 
slight variations, but these, among the many, cannot be taken 
for a new species. 
Docidium occidentale, n. sp. Mr. Turner acknowledges to have 
seen but one-half of a cell of this Desmid. A new species on so 
slender a basis cannot be relied upon. Had he seen a fractional 
part of the hundreds which came under my observation, he 
would not have ventured a new name for D. gracile, Bail. 
Staurastrum gladiosum, n. sp.—I fail to see how this form can 
be separated from S. echinatum, which is by no means a rare 
species, but varies considerably. 
Euastrum pseudo-elegans,n. sp.—£. elegans is one of. our 
most common forms of the genus; varieties are without number. 
Euastrum coronatum, n.sp., appears to be simply a large 
form of £. simplex. 
Cosmarium gemmatum, n. sp.—This is nothing more than a 
poor, imperfectly developed form of C. ¢riplicatum, common in 
ponds near Minneapolis, Minn.; seldom as finely formed as in 
localities nearer the Atlantic. 
Micrasterias mamillata, n. sp., was found in the same small 
cove in which JV. apiculata abounds, and appears to be a form of 
that species. 
The following: Genicularia Americana, n.sp.; Penium spiro- 
striolatum, Barker; Gonatozygon sexspiniferum, Nn. sp., are forms 
I do not know, and for the present accept as new to our flora. 
Of the value of the many varieties recorded I will say noth- 
ing, but merely make these general remarks. In the study of the 
Desmids, as in the study of other plants, the fact must not be 
overlooked, that none are subject to the mathematical rules 
of preciseness which govern the astronomer or the engineer 
in his calculations. Large allowances must be made for varia- 
tions in the size and form. Two leaves from the same tree, or 
two roses from the same bush, will scarcely be found absolutely 
alike. Plants derived from seed out of the same pod may vary 
greatly, yet they will retain their specific characteristics. 
For an idea of the variations among Desmids, reference may 
be made to Plate XXX., (Des. U. S.), eight quarter-cells of 4. 
Torreyi; Plate XXXI., M. radiosa ; Plate XXXVIIL., M7. truncata, 
Patient study and unwearied examinations can alone decide 
