164 BRITISH DESMIDIEiE. 



the present as the plant of Nitzsch, whilst the figure m Kiitzing's 'Synopsis 

 Diatomearum' must be referred to C. moniliferum. 



Length of frond -^ of an inch ; greatest breadth ■^\^. 



Tab. XXVII. fig. 1. a. front ^dew ; b. side view. 



2. C. acerosum (Schrank) ; frond linear- lanceolate, gradually tapering ; 

 ends conical ; fillets distinct ; vesicles in a single series ; empty frond 

 colourless; striae none or indistinct. 



/3. Frond more elongated ; strite more distinct. 



Vibrio acerosus, Schrank, Faun. Boiea, 3. 2. p. 47 (1803). 



Clostemim acerosum, Ehrenberg, Abhandl. der Berl. Ahademie (1831) ; 

 Infiis. p. 92. t. 6. f. 1. Meneghini, Synop. JDesmid. in Linncea 1840, 

 p. 233. Kiitzing, Phycoloyia Germanica, p. 131. Jenner, Fl. of Tun- 

 bridge Wells, p. 196. Hassall, British Freshwater Algce, p. 374. 



Carnarvon ; Dolgelley ; and Penzance, J. R. Several stations in Sussex, 

 and near Reigate, Surrey, Mr. Jenner. Cheshire and Westmoreland, Mr. 

 Sidebotham. Manchester, Mr. WiUiainson. Aberdeenshire and Banffshire, 

 Mr. P. Grant. Bristol, Mr. Thwaites. 



jS. Brackish water at Shirehampton, near Bristol, Mr. Thwaites. Ger- 

 many, Fhrenherg, Kiitzing. Falaise, Brebisson. Mexico, Bailey. 



Frond bright green, slender, six to twelve times longer than broad, linear- 

 lanceolate ; ends conical ; lower margin nearly straight, except at the extremi- 

 ties, the conical form of which causes it to incline upwards ; the upper margin 

 slightly convex. Fillets three or more ; vesicles arranged in a single longitu- 

 dinal series. 



The empty frond is colourless, and has a transverse line at the suture. This 

 species is generally described as destitute of strise ; but Mr. Jenner and myself 

 have frequently detected them, although seldom distinctly. The striae are 

 more evident in some specimens of /3. 



Sporangia have been gathered by Mr. Jenner in Sussex ; they are orbicular, 

 and placed between the deciduous fronds. 



Closterium acerosum differs from C Lunula and C lanceolatum in its more 

 slender frond. Some states of it approach nearer to C. turgidum ; it is usually 

 however more slender, and its empty frond also is colourless, and its strise, 

 whenever they occur, are very indistinct. 



Length of frond from yJ-g to -^ of axi inch ; greatest breadth from xiws ^^ 

 g-iy ; diameter of sporangium xsr- 



Length of variety /3. from A ^^ T2 5 greatest breadth -^. 



Tab. XXVII. fig. 2. a. front view of frond with endochrome ; e,f,g. small 

 states ; b, d. empty fronds ; h, i. conjugating fronds ; k, I. perfect sporangia ; 

 m. germinated capsule ? ; e. frond of /3. 



3. C. lanceolatum (Kiitz.) ; frond semilanceolate, gradually tapering ; 

 ends subacute ; fillets several ; vesicles in a single series ; empty 

 frond colourless. 



Cymbella Hophirldi, Moore, in Harvey's Manual of British Algce, p. 215 

 (scarcely Conferva ovalis, Hopkirk.) (1841). 



