256 ARCHER, ON A NEW SPECIES OF ANKISTRODESMUS. 



paragraph wliicli I, as previouslj'^; head " Affinities and dif- 

 ferences." 



Genus — Ankistrodesmus, Corda. 



General characters. — Cells minute, smooth, elongated, 

 attenuated, more or less numerously aggregated, forming 

 fasciculi or families, each family resulting from the self- 

 division of a single cell, which commences by the formation 

 of a somewhat oblique septum at the middle, continually 

 rendered more and more oblique from the young cells growing 

 alongside one another longitudinally until they each attain 

 the length of the original parent cell, the process being again 

 and again repeated by each, till the aggregated family consists 

 of at most thirty-two cells, the family finally again breaking 

 up into single cells (Nageli) .* 



Ankistrodesmus acutissimus, mihi. 



Specific characters. — Cells fusiform, straight, very slender, 

 gradually tapering, very acute. 



Locality. — I have noticed this curious little production for 

 two successive 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 (nuclear?), pale body or space 

 placed near the middle of the cell (that is, equidistantly from 

 each end, but close to one side), otherwise usually apparently 

 homogeneous, sometimes slightly granular. 



Measurements. — Length of cells, -^ to -^^ ; breadth, 

 to -r .. ,', „ „ of an inch. 



I) "" 1 1 II u 



Plate XII, figs. 44 to 56, mature and dividing fronds; 

 fig. 57, for some time mounted in '^Thwaite's fluid." All 

 magnified 400 diameters. 



Affinities and differences. — I have no doubt but that the 

 plant at present under consideration is identical with Closte- 

 rium subtile, Breb.,t and, I am strongly inclined to suspect, 

 also with Closterium Griffithii, Berk.; J hence, of course, that 

 those writers have described one and the same thing under 

 the names mentioned. Neither author, however, has de- 

 scribed or figured the mode of cell-division in his specimens, 



* 'Gattungen einzelliger Algen,' pp. 82, 83. 



■f 'Liste de Desmidiees observecs en Basse-Normandie,' p. 155. 



X 'Annals of Natural History/ 2nd ser., vol. xiii, p. 25G. 



