DUBLIN UNIVERSITY ZOOLOGICAL AND BOTANICAL ASSOCIATION. 235 
For the reception of two of the new forms to which I think I am 
the first to direct attention, I now venture to form a new genus; and, 
while opposed (as I should undoubtedly he) to the formation of unne¬ 
cessary generic characters and names, I do not think that in proposing 
a new genus, I have, in the present instance, fallen into so grave an 
error. I admit I am myself inclined to think it true that genera, like 
species, have an existence in nature,—an opinion held, I imagine, by 
the minority; however, there can he no doubt that many of the genera 
of our systems cannot be strictly natural, and this perhaps sometimes 
arising from a desire to divide into two or three other genera, possibly 
a good and natural genus, merely because, containing numerous species, 
it is thought too cumbrous and unmanageable, or from the natural and 
true characters limiting each genus not having been arrived at. In 
the Desmidiaceae the distinctive characters of the genera are usually 
sufficiently well marked and decided; while, with two exceptions of 
genera, each containing only one species, they are formed of often nu¬ 
merous species, embodying and presenting, in, generally, an obvious 
manner, the characters of the genus under which they fall. I think, 
then, it is repugnant to a proper classification to unite in any genus, the 
species of which in an evident manner, by the possession of common 
characteristics, form a natural assemblage, one or more other species 
(although as a matter of course there must he minor points of affinity) 
which positive and negative characters of form and habit, it may he 
slight, but decided, and not held in common with the true species of the 
genus, exclude from being therein embraced. 
A belief in the correctness of the opinion I here endeavour to express 
has emboldened me to the step which in this paper I now venture to 
take, in an attempt to form a new genus, and which I do with much 
diffidence; for, being wholly without the guidance of any of our masters 
in the study of these minute Algae, or the benefit of their opinion, I 
would put forward the following, rather as suggestive than conclusive, 
more in the hope of, perhaps, ultimately eliciting information and cor¬ 
rection, than as indisputably settling the position of the forms presently 
to be described. 
It will, perhaps, he more convenient that I first proceed to describe 
the new forms which I have met with, one of which belongs to the genus 
Sphaerozosma, another to Staurastrum, while the remaining two fall 
under the proposed new genus; and then to enumerate the species as de¬ 
scribed in Halts’ monograph supplementary to my former catalogue, in¬ 
cluding therewith those species now for the first time noticed. 
Before drawing attention to the new forms, however, it has been 
suggested to me, in deference to those of this Association (as well as to 
those who may hereafter favour this paper with a perusal) who, not 
having immediate access to Haifa’, or the “ Micrographic Dictionary,” 
&c., or not having directed their attention to the organisms themselves, 
may he comparatively unacquainted with the Desmidiaceae, or kindred 
minute Algae, that a short account of their nature and position in the 
vegetable kingdom may not he uninteresting ; and while endeavouring 
