206 ARCHER, ON CYLINDROCYSTIS, 
been in many respects, or on the whole, quite a hopeless one. 
Nor do I think, so far as I can see, that the breaking up of 
the species of the genus Palmogloea which fall under’ Cylin- 
drocystis, Mesotzenium, and Spirotzenia, has been quite un- 
successful ; nor can I see how the advisability of the step 
can in itself be adduced as an argument as to the uncertainty 
of those forms, but should rather regard it as a natural conse- 
quence of their characters being happily better established ; the 
others formerly included in Palmoglcea have to be carried else- 
where—one, I think, at least, to Chroceoccacez ; and their true 
nature, I quite admit, does not seem at all so well established. 
Further, Dr. Hicks goes on to remark—‘‘If by one ob- 
server the envelope of mucoid matter be taken as a specific 
or even generic sign—if the mode of segmentation be taken 
by another as of specific or generic value—if the size of the 
cell, or the position of the nucleus, or the mode of diffusion 
of the endochrome within the cell, be sufficient in the eyes 
of another to separate genera—if, as Mr. Archer contends, 
the oval shape is another important distinction—it seems to 
me no wonder that the difficulty acknowledged by all has 
arisen.” These remarks are intended to be applied to the 
genus Palmogloea; and I quite acquiesce with their author, 
that no wonder the difficulty adverted to should have arisen, 
when each single observer pays attention to one only of such 
characteristics, disregarding all the rest. The genera Cylin- 
drocystis, Mesotzenium, and Spirotznia (which are those in 
question), each, it is true, possesses an envelope of mucoid 
matter, but it indeed exists also in many Palmellacez, as well 
as Chroococcacez, likewise in Desmidiacee, &c. The trans- 
verse mode of segmentation—that is, through the shorter 
diameter—occurring in these genera, takes place also in Des- 
midiaceze, in the elongate forms of Palmellacez, as well as 
of Chroococcacee. The oval shape, too, is shared by the 
forms in question with several other forms in both those 
families. The size of the cell likewise varies in these plants, 
within certain limits, in the same species. The nucleus is 
very hard to be made out—indeed, I doubt if it is always to 
be perceived or existent even in Palmellacez. Nevertheless, 
I hold that the forms in question are abundantly distinct ; 
and that, when the eye becomes familiarised with them, they 
can beat once recognised. It is, of course, here as elsewhere, 
on the special characters possessed in common by certain 
groups of the species, combined with certain of the foregoing 
general characters, and not upon any one or more of the 
general chaaacters, as suggested by Dr. Hicks, that we must 
rely as of generic value, and on the ultimate individual proper 
