342 Mr. J. Ralfs on the Nostochinee. 
Aphanizomenon cyaneum differs from A. Flos-aque by its stra- 
tum not appearing flocculose, by its paler inconspicuous filaments, 
which do not cohere in lamine, and would often escape detection 
under the microscope but for the presence of the sporangium, 
which has a far broader hyaline covering in this than in the latter 
species. 
Puate IX. fig. 7. Filament highly magnified. 
3. A. incurvum (Morren). ‘ Filaments articulated, cohering together 
in flat laminze, laciniated at the apex; articulations two to eight 
times longer than broad.” Trichodesmium Flos-aque, Ehrenb. in 
Poggend. Annal. 1830, p. 168 (according to Kiitzing). Aphani- 
_zomenon tncurvum, Morren in Memoir (1837) ; Thompson in An- 
nals of Nat. Hist. vol. v. p. 82; Harvey, Manual of Brit. Algz, 
p- 145; Hassall, Brit. Freshwater Algze, p. 280. t. 76. fig.6. Lim- 
nochlide Flos-aque y. Harveyana, Kitzing, Species Algarum, 
p- 286 (1849) ; Tabule Phycologice, t. 91. fig. 2. 
Ballydrain Lake, Mr. W. Thompson ; Lough Neagh, Mr. D. Moore. 
Belgium, Morren ; Germany, Kiitzing. 
I regret that I am unable to afford any satisfactory informa- 
tion respecting this plant, for although Mr. Thompson has sup- 
plied me with specimens, they are unfortunately preserved upon 
paper, and could not be removed in a condition fit for examination. 
Respecting the Ballydrain species, one would suppose there could 
be no reasonable doubt as Dr. Morren has determined it. Still 
it is very possible that his Aphanizomenon incurvum has been 
rightly supposed by Kiitzing to be merely the Flos-aque, for 
nothing in the descriptions renders the opinion improbable. The 
Dublin plant at least is decidedly the A. Flos-aque. Mr. Thomp- 
son’s A. mncurvum however differs materially from all my speci- 
mens of the A. Flos-aque both in colour and in the form of the 
particles, which are circular and dot-like, very unlike the larger 
and lobed flakes of the other. Mr. Hassall’s figure represents 
the filaments as tapering—a character, indeed, amply sufficient 
to distinguish the A. incurvum from the preceding species ; but 
unfortunately, if the filaments really possess this character, 
neither Dr. Morren nor Mr. Hassall have noticed it in their de- 
scriptions, and so the matter is still in doubt. 
Since the above was written, I have received from Mr. Moore 
some specimens better suited for examination. Although not 
from the same station as Mr. Thompson’s plant, they exactly 
agree with it in appearance ; the specks are unlike any other spe- 
cies that I have seen, and in form as well as in size and scattered 
habit resemble the small dots made by house-flies. Under the 
microscope the filaments appear parallel; they do not closely 
cohere as in 4. Flos-aque, but are rather held together by the 
