220 ARCHER, ON CYLINDROCYSTIS, 
explains that by “every variety of conditions” he means 
“in widely remote localities.” It will be admitted, I think, 
that the West, Centre, and North of Europe are widely 
remote localities; yet from these far-apart sources the same 
Desmidian forms have been collected, maintaining their 
special characters. In his lately published list of Des- 
midiacez collected in Sweden, Cleve,* while he truly enough 
says the specific distinctions are often founded on minute 
differences, states that he never found any difficulty im 
identifying the forms he met with with those of other 
countries by aid of dried specimens and figures, and he 
enumerates a goodly catalogue. I myself have seen some 
examples from other parts of Europe. Nay, I may appeal 
to Dr. Wallich’s paper on Desmidiaceze collected in Bengal,+ 
where he recognises, and is able to name from their own 
special inherent intrinsic characters, several of the species 
belonging to Britain; thus, not only from still more widely 
remote localities, but under circumstances of climate greatly 
varying from that in which the same species occur here. It 
is true that, in regard to several of the forms which I should 
be disposed to regard as abundantly distinct, Dr. Wallich 
would often combine several of such into a single species, 
under a common specific designation; but yet this does not 
militate against this part of my argument, for he was still 
able to identify the forms by their intrinsic characters there 
as here, although he holds a different view from that which 
I have hitherto found myself compelled to adopt, as to the 
value of those characters. 
Dr. Wallich thinks, “that in these forms such differences 
as the number of indentations, the acuteness or obtuseness 
of the teeth, the number of spinous processes, and so forth, 
indicate mere accidental variations.” But these very cha- 
racters, thus succinctly recapitulated, according to the degree 
and mode in which they are presented, are amongst the most 
available holdpoints for the discrimination, not of species 
alone, but also of genera. In what does a Micrasterias 
differ from a Euastrum, a Staurastrum from a Cosmarium, 
&c. &c., but in the mode and way, the degree and extent, in 
which these characters, and characters such as these, are 
presented—not to speak of the various forms within those 
genera which Dr. Wallich goes so far as to allow are really 
good species. Dr. Wallich, for instance, calls such forms as 
* Cleve, “ Bidrag till Kannedomen om Sveriges séttvattensalger af familjen 
Desmidiee,” in ‘Ofversigt af Kongl. Ventenskaps-Akademiens Forhand- 
lingar;’ Stockholm, 1865, p. 481. 
+ ‘Annals of Nat. Hist.,’ 3rd ser., vol. v, pp. 184, 273. 
