128 PROCEEDINGS OF SOCIETIES. 
irregularly shaped families, seemingly owing to the development 
of the delicate supporting fibre not going on in the same regular 
manner as in D. Hhrenbergianwm ; and the cells themselves are 
much larger, and are reniform. In the form now exhibited by 
Mr. Archer the aggregate family is larger than in either of the 
foregoing, and the branching of the fibre less regular than in 
D. Ehrenbergianum, and seemingly more so (to judge from the 
figure) than in D. reniforme. The total family sometimes acquires 
a divergent or lobed character, owing to the fibre or thread, on 
the subdivision of the original cell of the family, becoming drawn 
out to a greater extent than during subsequent growth, thus the 
cells of the second generation becoming further pushed away from 
one another than is the case in the subsequent generations. Thus, 
the aggregate family may appear like twin families, or, as it were, 
as if certain portions or branches of it had started from two or 
sometimes more fresh centres. The cells themselves, moreover, 
were neither elliptic, as in D. Hhrenbergianum, nor reniform, as in 
D. reniforme; but they are somewhat irregularly figure-of-8- 
shaped, that is, constricted at both sides, the ends tapering in 
a somewhat triangular manner to the bluntly rounded extre- 
mities; they are, besides, larger than either of the preceding, 
much larger than those of the first. This plant is, indeed, 
wholly different from, yet congeneric with, both. It might, indeed, 
suggest itself, from the fact of the cells being seated at the 
summits of the branches of a delicate thread-like stipes, and 
their being constricted, that this plant might belong to De Bré- 
bisson’s genus Cosmocladium ; but in that plant the stipes is 
thick and broad, and the aggregate colony forms a dendroid struc- 
ture seated epiphytically on Confervoids, not freely swimming, 
and the growth radiating from a common original centre. Still, 
there must, perhaps, be a certain amount of affinity; yet there 
can be no doubt but that Mr. Archer’s plant far more properly 
belongs to Dictyospherium (Nag.) than to Cosmocladium (Bréb.). 
Be, then, this growth a species or a form, be it swe generis or but 
a transitional state of some other species—a question which it 
would be at present impossible to decide—the present plant is 
quite as well marked as either of the two previously described, 
and therefore quite as worthy of arecord. As to the nature of 
the curious dichotomous, extremely delicate, fibre-like stipes in 
this genus on which the cells are borne, Mr. Archer found it 
impossible to throw any light. So delicate is it that it often 
requires a peculiar illumination to perceive it properly; but so 
constant and so peculiar a character must have some signification, 
and seems to give the minute alge possessing it a special generic 
type, and, pending more knowledge as to their origin and nature, 
a claim to be accorded a special generic rank. 
Dr. John Barker exhibited a minute Cosmarium gathered by 
him on the occasion of the Club excursion to Lugnaquilla, which, 
with the information at disposal, he was inclined to regard as 
Cosmarium quadratum, or a small variety of that species. It is 
