248 
PROCEEDINGS OF SOCIETIES. 
evitable that the growing segments should be at first smaller and nar¬ 
rower than the older ones; in the form under consideration, however, 
the nascent segment has only to grow longitudinally to form a continuous 
cylinder with the opposite older segment. Having thus (at least to my 
own satisfaction), even without this last conclusive evidence, proved 
the form, of which I hope I have succeeded in conveying a satisfactory 
conception, to be a true Desmidian, of which group there can be no 
doubt it is a new species, I will now assume both these points conceded, 
when the next question becomes—to what genus of Desmidiaceee does 
this plant belong ? Confining our attention for a moment to a single 
joint, it might seem to possess as good a right to a place in the genus 
Docidium as Docidium asperum {Breb.), as described in Ealfs, but I shall 
presently give, I believe, valid reasons, why I think neither of these or¬ 
ganisms would be rightly placed in Docidium, and, if not in that genus, 
certainly not in any other known. 
On a former occasion, when I had the honour to lay before the As¬ 
sociation the first part of a Catalogue of Dublin Desmidiacese, I appended 
to the mention of Docidium, asperum {Breb.) a note of my having met 
that species forming short filaments. How, I have since, on several 
occasions during last summer, met with it, and always forming fila¬ 
ments of indefinite length, but being usually mixed with other Algae, 
never in very large quantity; frequently, however,, detached cells occur, 
more especially when kept some time in the house. In addition to the 
fact of this species forming filaments, which is not alluded to in Ealfs, I 
have met specimens possessing, when fresh, in nearly every joint, a pale 
central space or division of the endochrome into two equal portions, and 
contracted in an irregular manner enclosing a single central series of cor¬ 
puscles, somewhat like the side or edge view of the endochrome of the 
form to which I first directed attention, and sometimes disposed in a 
zigzag or subspiral manner, while possessing all the other characteristics, 
as described in Ealfs: I allude to the roughness, owing to minute scat¬ 
tered granules, and to the dilated extremities (Fig. 5). There can be no 
doubt whatever that it is the same plant. When a joint is fractured, it 
breaks at the middle, but not with so smooth a line of fracture as the before 
described form. There has also occurred to me another form nearly allied 
to Docidium asperum , but I believe a distinct species, being altogether a 
smaller and more slender plant, and of a different outline (Fig. 6). This 
form, too, occurs filamentous, but is very fragile. It differs from Doci¬ 
dium dsperum {Breb.) in each joint being fusiform, at the middle of 
which, where it is broadest, it is little more than one-half the diameter 
of that species, whence it gradually tapers towards the extremities, 
which become somewhat suddenly dilated, giving to the ends a slightly 
capitate appearance. It, too, is rough on the surface with minute scat¬ 
tered granules. I think this form differs materially from the variety of 
Docidium asperum figured in Ealfs after M. de Brebisson, which is quite 
as large a plant both in the diameter and length of the cells as that spe¬ 
cies, which are not at all fusiform, and, differ only in the extremities 
being somewhat constricted beneath the apex. I have found this fusi* 
