250 
PEOCEEDINGS OP SOCIETIES. 
under consideration resemble the apparently natural genus Docidium, as 
at present constituted. The same considerations will, I think, distin¬ 
guish any of these forms from Penium. There is, perhaps, some resem¬ 
blance, in a separated joint, to such forms as Penium truncatum or 
Penium cylindrus , but the ends in both these species are rather rotundato- 
truncate than truncate, while it seems that the affinities of Penium are 
rather with the Palmellaceous Algae, through such species as Penium 
Brebissonii, whereas I apprehend the forms now described approach the 
Zygnemaceous Algae. 
These are, then, I believe, filamentous Desmidiacese, the individual 
joints of which bear some resemblance to Docidium (still less to Penium 
and Closterium), while the filament does not resemble any other estab¬ 
lished filamentous genus. I believe, then, the first described form must 
be taken as the type of a new genus, and which, so far as I know, will 
be the only example of a fixed or attached Desmid; along with which 
I would venture to associate Docidium asperum (Breb .), and, as a matter 
of course, the fusiform species. To some it may, perhaps, seem prema¬ 
ture to found a genus upon the characters presented by the mature form 
alone, without acquaintance with the reproductive state. But it will be 
recollected that none of the genera, according to Balfs, are founded upon 
any appearance or phenomenon presented by the mode of conjugation, 
or form of the sporangium, and it is rarely employed as a specific cha¬ 
racter; and this, for necessary and obvious reasons: the sporangia of 
numerous species are not known, in many but rarely met with, while 
in the same genus considerable diversity sometimes occurs in the sporan¬ 
gium, such as the form of the spines and other particulars. Por my own 
share, I do not see any course open but to make a new genus. Prom 
the simplicity of form, however, I have found some difficulty in draw¬ 
ing up concise characters: I trust, however, the following may be found 
to meet the requirements of the case:— 
Class.—ALG-iE. 
Order.— Chloeospoee2e or Coxeeevoide^i. 
Pamily.— Desmidiaceje. 
Leptocystixema {nov. gen.). 
Plant an elongated jointed filament (often separating); joints straight, 
much elongated and slender, without a central constriction or inflation, 
entire, ends simply truncate, or dilated and truncate (no evident gela¬ 
tinous sheath). 
1 .—leptocystinema Kinahani {nov. sp.). 
Pilaments attached, frequently breaking up into separate joints, 
which are slender, extremely elongate, linear, cylindrical, and smooth, 
their ends abruptly truncate; the junction of the halves marked by a 
