ARCHER, ON TWO NEW SPECIES OF COSMARIUM. 181 
be some who, on looking at the mature unconjugated condi- 
tion only of this little plant, on account of its simple form 
and minute size, would be disposed to regard it merely as an 
indescribable nonentity—perhaps a dwindled or staryed ex- 
ample of some other form—or, at best, as only a transitional 
or gradational variety. It is true that, like many of its im- 
mediate allies, it is only a minute, elliptic, or, as I have tried 
to describe it, barrel-shaped cell; nevertheless, the first 
moment I noticed it, even in its unconjugated state, I 
thought not so, but felt that it was indeed a new form, which 
I had never seen before. 
It is distinctly a species of Penium, Bréb., the structure of 
its cell-contents removing it from Cylindrocystis, Menegh., 
or Mesotenium, Nig.,—the entire want of a central con- 
striction separating it from certain species of Cosmarium, 
Corda,—the same, as well as the want of a terminal notch, 
placing it apart from Tetmemorus, Ralfs. I do not believe 
that it can be mistaken for any other species in the genus 
Penium, its minute size alone readily distinguishing it. Ir- 
respective of its minuteness, there is no other species of 
Penium in which the length of the cell is so short in propor- 
tion to its width, all other species, with the exception of P. 
(Dysphinctium) annulatum, Nag., being several times longer 
than broad, while the species just referred to is about twice 
as long as broad. And this relationship of comparative 
length and breadth I believe to be in this family a by no 
means unimportant character, though undoubtedly of so little 
value in others. Nor would I wish to be understood that 
here even this character is decisive; but when it is found 
that a pretty constant steadiness of relative length and breadth 
of most species is associated with other characters, it becomes, 
I think, a useful and readily applied diagnostic distinction, 
ancillary but subservient to other more special ones. From 
Penium annulatum, Nig., then, besides its less comparative 
length, this species is distinguished by its non-cylindrical 
outline and smooth cell-membrane. From P. Navicula, 
Bréb., this species is distinguished by its less comparative 
length, and by its broadly elliptic or barrel-shaped, not navi- 
cular, cells, and by the want of a terminal clear space with 
moving granules. There is no other Penium for which it 
could possibly be mistaken. 
From Cosmarium curtum, Bréb., it is distinguished by its 
shorter comparative length, and the entire want of a con- 
striction, by its broadly elliptic, not attenuated, ovate outline, 
and by the “ fiilets”’ of the endochrome being far less de- 
cidedly marked. From Cosmariwm cucurbita, Bréb., it is 
