404 Mr. J. Ralfs on the British Desmidiese. 



the free extremity, and subacute or rounded at the inner one. As 

 the cells are not placed evenly, but each projects beyond its neigh- 

 bour, each row is oblique ; their position with respect to each 

 other is such that the inner ends of two cells of the lower lie be- 

 tween those of the upper row, whilst that of the third is outside 

 the end of the highest in the upper. Of the two remaining cells, 

 which are lunulate, one is placed beyond the outer cell in each 

 series, and is therefore not in contact with any cell in the other. 

 They however take the same direction as the other cells in the 

 series to which they respectively belong. 



Meneghini, under his Scenedesmus triseriatus, refers to the 

 figures a, b, e of the Arthrodesmus acutus of Ehrenberg. Mr. Berke- 

 ley is convinced that our plant is represented in fig. b. In this 

 opinion I fully concur; but I have great doubt whether it be di- 

 stinct from the Scenedesmus obliguus, Kutz., and by Ehrenberg 

 both are considered as states of S. acutus. It however seems di- 

 stinct from the S. acutus, as it has all the cells in a series closely 

 united ; but in all these plants their form is nearly the same, and 

 I have not sufficient experience to decide whether any interme- 

 diate arrangements of them may be found. 



If distmct from S. obliguus, it must be distinguished by the 

 outer cells being lunulate and the extremities of all more acute, 

 for in Turpin's figure of the obliquus the cells are arranged in the 

 same manner as in our plant. I strongly suspect that a better 

 acquaintance w"ith them will prove the necessity of uniting these 

 forms. I subjoin the descriptions of both from Meneghini. 



" S. triseriatus, Mgh., cellulis fusiformibus exilibus octo, apicibus acutis, 

 duobus medianis rectis, caeteris extrorsum lunulatis in seriein triplicem al- 

 ternantibus, quarum mediana a duabiis extimis formata." 



" S. obliqmts, Kutz., cellulis elliptico-fusiformibus octonis, extremitatibus 

 rotundatis, in seriem duplicem obliquam dispositis. Kutx. /. c. p. 81 ; Ach- 

 natithes obliqua, Turp." Menegh. I. c. p. 208. 



Plate XII. fig. 7. Scenedesmus triseriatus. 



5.'S. ohtusus, Meyen. Cells three to eight, ovate or oblong, with 

 rounded ends and arranged alternately in two rows. Menegh. /. c. 

 p. 208. Scenedesmus quadraltermis, Kutz. /. c. p. 608. fig. 94. 

 Scenedesmus octalternus, Kutz. I. c. p. 609. fig. 95. Arthrodesmus 

 acutus, Bailey, American Bacil. fig. 18 .^ 

 In boggy pools, DolgelLey. 



Fronds minute, composed of from three to eight ovate or ovato- 

 oblong cells, arranged alternately in two rows. The endochrome 

 is veiy pale green. 



The specimens I have examined did not agree in every respect 

 with the description and figures of this species, but they probably 

 belonged to it. The cells were ovate, the broad ends of the rows 

 placed alternately, the smaller ends being in difi'erent directions ; 



