192 BRITISH DESMIDIE^. 



the cells form only a single series, which is nevertheless irregular on account 

 of the alternate projection of the cells in opposite directions. In S. ohliquus, 

 on the other hand, the cells by division form two distinct rows, which, after 

 separation, become two fronds. 



Length of cell from y^^ to -^^^0 ^f an inch ; breadth from -g^ig^ to j-gVr- 

 Tab. XXXI. fig. 14. perfect frond. Tab. XXXIV. fig. 16. distorted variety. 



4. S. ohliquus (Turpin) ; cells elliptico-fusiform, after division arranged 

 in two distinct, generally oblique series, the outermost cell of each 

 not in contact with any of those in the other series. 



Achnanthes ohliqua, Turpin, Bid. des Sc. Nat. par Lew. Atl. Veg. ves. f. 9 



(1820) ; Mem. du Mus. v. 16. t. 13. f. 9. 

 Scenedesmus obliquus, Klltzing, Synop. Diatom, ifi Linncea 1833, p. 609. 



Meneghini, Si/)iop. Besmid. in Linncea 1840, p. 208. Berkeley, English 



Botany, t. 2933. 

 Scenedesmus triseriatus, Meneghini, Conspect. Alg. Eugan. p. 18 (1837) ; 

 - Synop. Besmid. in Linncea 1840, p. 208. Ralfs, Annals of Nat. Hist. 



V. 15. p. 403. t. 12. f. 7; Trans, of Bot. Soc. of Edinburgh, v. 2. p. 161. 



t. 15. 

 Arthrodesnms acutus, Ehrenberg, Infusor. t. 10. f. 19. 6 (1838). 



King's Cliffe, Rev. M. J. Berkeley. Near Bristol, Mr. Thwaites. Ayrshire, 

 Rev. B. Landsborough. Near Manchester, Mr. Sidebotham. Dolgelley and 

 Penzance, J. R. Near Aberdeen, Mr. P. Grant and Br. Bickie. Storrington, 

 Sussex ; and Weston Bogs near Southampton, Mr. Jenner. 



Germany, Kiitsing, Ehrenberg. Italy, Meneghini. Falaise, Brebisson. 



Scenedesmus obliquus approaches very closely to Scenedesmus acutus, and 

 the principal distinction depends on the different appearances presented by the 

 dividing frond ; and as this plant is most commonly seen in that state, I shall 

 so describe it, merely premising that when separated, the frond consists of 

 only one row. Mr. Berkeley has united S. triseriatus to S. obliquus, and I 

 readily follow his example. 



The cells are eight in immber, arranged obliquely in two distinct series. 

 Each series has three cells, which are fusiform, equal, somewhat veutricose in 

 the middle, acute at 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, the rows are oblique ; their position with respect to each other is such 

 that the inner ends of two cells of the lower lie between 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 lunate, 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. 



The different species of Scenedesmus frequently make their appearance in 

 clear water that is kept in glasses or bottles and exposed to the light. I have 

 received specimens of this species collected in this manner from Mr. Lands- 

 borough and Mr. Berkeley, and have myself repeatedly noticed its appearance 

 in bottles containing other Desmidiese, and sometimes its rapid increase so as 



