70 PROCEEDINGS OF SOCIETIES, 
filaments a remarkable and exceedingly pretty moniliform appear- 
ance. 
Tn continuation, Mr. Archer dilated at some length on the cha- 
racters which seemingly hold good as specific marks in this in- 
teresting genus, thanks to Pringsheim’s masterly researches; ex- 
pressing his regret likewise that authors continue to describe 
species on the false characters of length and breadth of cells, and 
such like. It would seem far better wholly to omit them from 
descriptive works than to insert these spurious species, or at least, 
species some of which may be good, though inadequately charac- 
terised, owing to the real, though more recondite, specific charac- 
ters being ignored. It is to be regretted that Rabenhorst’s 
in most respects so exceedingly valuable work, ‘ Kryptogamen- 
Flora von Sachsen,’ &c., is, as regards this genus and Bulbochete, 
no exception to this fault. But, in expressing this opinion, Mr, 
Archer would not wish to be supposed to hold the characters de- 
ducible from the comparative dimensions of the joints in this genus 
to be quite valueless. Within certain limits, and in a secondary 
point of view, they are doubtless of importance, although here, as 
is well known, varied comparative dimensions of cells occur in one 
and the same filament. For instance, even any isolated jot from 
a barren filament of the present plant could never be supposed to 
belong to, nor be mistaken for, a joint of Gdogonium Itzigsohnit. 
The former is amongst the largest, both in length and width (which, 
indeed, vary amongst themselves within their own limits) ; the latter 
is amongst the smallest, the joints not varying greatly in width, 
which is always very slight. 
Mr. Archer would quite coincide with Professor Pringsheim’s 
opinion, that the genus Psichohormium (Kiitzing) was likewise 
founded on false characters, and that the mineral incrustation of 
the filaments on which this genus was founded, is, as a character, 
quite untenable. He thought Gdogoniwm twmidulwm very prone 
to this condition ; and it does not seem impossible that other forms 
not belonging to Gidogonium might acquire this extraneous coat- 
ing, and so be by Kiitzing placed under his false genus Psicho- 
hormium. 
In two places in his beautiful memoir Professor Pringsheim 
promises to give a more detailed systematic description of the 
species known to him of the two genera (idogonium and Bulbo- 
chete, and it is greatly to be wished that he should redeem that 
promise ; however, what he has given beautifully shows the plan 
which should be followed in studying these forms; and though they 
are more recondite than those superficial characters usually had 
recourse to, he has shown us the points upon which the true 
specific characters seem to depend, albeit one must trust to mostly 
a rare good fortune in finding the specimens in the condition in 
which those characters are fully displayed. 
Mr. Archer exhibited specimens of a Desmidian which, as far 
as he was aware, had not been found in Ireland—Cosmarium curtum 
