86 DUBLIN NATUEAL HISTORY SOCIETY. 



Anhistrodesmus acuUssimm (mihi). 



Specific Characters: — Cells fusiform, straight, yery slender, gradually 

 tapering, very acnte. 



Locality : — I have noticed this curious little production for two suc- 

 cessive years in bog-water kept for some time in the house, and obtained 

 from pools in the Dublin Mountains. 



General Description : — Cells very minute, twenty to twenty -five 

 times longer than broad, fusiform, very slender, straight, very acutely 

 acicular, solitary, or forming fasciculi of two or four cells ; endochrome 

 light-green, mostly with a minute parietal semicircular or rounded (nu- 

 clear ?) pale body or space placed near the middle of the cell (that is, 

 equidistantly from each end, but close to one side), otherwise usually ap- 

 parently homogeneous, sometimes slightly granular. 



Measurements : — Length of cells, j^^ to j^q ; breadth, y^g^oo ^^ 

 TOoo ofaninch. 



Plate II., Figs. 44 to 56, mature and dividing fronds ; Pig. 57, for 

 some time mounted in " Thwaite's fluid," all magnified 400 diameters. 



Affinities and Difi'erences : — I have no doubt but that the plant at 

 -present under consideration is identical with Closterium subtile (Breb.)* 

 and, I am strongly inclined to suspect, also with Closterium Griffithii 

 (Berk. ); f hence, of course that those writers have described one and the same 

 thing under the names mentioned. IN'either author, however, has de^^ 

 scribed or figured the mode of cell-division in his specimens — a charac- 

 ter, as I apprehend, of primary importance in separating Closterium 

 from Ankistrodesmus. Conceiving that I am right in supposing my 

 plant to be specifically identical with theirs, and as I think my account 

 of the cell-division to be correct, I believe I am justified in referring 

 the plant in question to Ankistrodesmus, and not to Closterium. To 

 adopt the plan I have pursued in regard to species, let us compare and 

 contrast for a moment the genera Closterium and Ankistrodesmus — the 

 latter genus, I think there can be no doubt, is quite equivalent to Ea- 

 phidium (Kg.); and I cannot see why Kiitzing should reject a prior 

 name. Closterium and Ankistrodesmus agree, then, in the cells having 

 an elongate, more or less attenuated, often arcuate, form ; but they differ 

 in several striking points. In the former genus there is always a pale 

 transverse band at the middle of the frond or cell, and arising from a sus- 

 pension or interruption of the denser endochrome at this region ; and this 

 pale space is apparent no matter what side of the frond is towards the 

 observer. In the latter genus there is, indeed, often a clear space at the 

 middle (as indicated in the form under consideration) ; but it seems to 

 me of a different nature. Here, in fresh specimens, it does not form a 

 transverse band, due to interruption of endochrome, but a rounded or semi- 

 circular or oblique smoothly defined spot, (of nuclear import ?), laterally 

 disposed, and closely approximated to the boimdary-wall — that is, eccen- 



* "Liste des Desmidiees observees en Basse-Normandie," p. 155. 

 t "Annala of Natural History," 2 Ser., vol. xiii., p. 25G. 



