BRITISH DESMIDIEiE. 61 



Traces of a mucous sheath have been detected by the Rev. M. J. 

 Berkeley and more recently by myself. 



A transverse view shows that the cell is triangular or quadrangular, 

 and that the endochrome has thick rays corresponding in number 

 with the angles; these rays are frequently cloven. 



Recent specimens of Desmidium are easily known from other 

 genera by one or two dark waved lines passing down the filament, 

 which appearance is occasioned by the twisting of the angular 

 filament. 



1 . D. Swartzii (Ag.) ; filament triangular, equal, with a single longi- 

 tudinal, waved, dark line formed by the third angle ; end view 

 triangular with the endochrome three-rayed. 



Biatoma Swartzii, Ag. Bisp. Alg. Svec. (1811). Lyngb. p. 177. t. 61. 



Besmidium Swartzii, Ag. Syst. p. 9 (1824). Consp. Crit. Biat. p. 56. Gre- 

 v-ille, Scot. Crijp. Fl. t. 292. Kiitziug, Synopsis Biatom. in Linncea 

 1833, p. 613 ; Phycologia Germ. p. 141. Greville in Hook. Brit. Fl. 

 V. 2. p. 402. Brebisson, Alg. Fal. p. 53. t. 2. Ehrenberg, Infus, 

 p. 140. t. 10. f. 8. Menegluni, Synop. Besmid. in Linncea 1840, p. 203. 

 Bailey, American Bacillaria in Amer. Journal of Science and Arts, v. 41. 

 p. 288. t. 1. f. 1. Harvey, Manual of Brit. Algce, p. 196. Corda, 

 Observ. Microscop. sur les Animal, de Carlsbad, p. 17. Ralfs, Annals 

 of Nat. Hist. V. 11. p. 375. t. 8. f. 3 ; Trans, of Bot. Soc. of Edin- 

 burgh, V. 2. p. 7. t. 2. Hassall, Brit. Freshwater Algce, p. 344. t. 83. 

 f. 7. 



Common. Appin, Capt. Carmichael. Tunbridge Wells, Mr. Bonder. 

 Swansea ; Carnarvon ; Dolgelley ; Penzance, &c., J. R. Many stations in 

 Sussex, and near Southampton, Mr. Jenner. Essex, Mr. Hassall. Caragh 

 Lake, Kerry, Mr. Atidrews. Meath, Mr. Moore. Westmoreland, Mr. Side- 

 botham. Rochdale, Mr. Coates. Manchester, Mr. Williamson. Aberdeen- 

 shire, Br. BicJcie and Mr. P. Grant. 



Sweden, Agardh. North Germany, Martens, Kiitzing and Ehrenberg. 

 Carlsbad ; Prague ; Reichenberg, Corda. Throughout the United States, 

 Bailey. Falaise, Brebisson. 



The filaments are elongated and very fragile, but separate spontaneously 

 mto single joints less readily than in Hyalotheca dissiliens and Bidymoprium 

 Grevillii. They adhere but slightly to paper. They are triangular, and, 

 when viewed under the lens, the margins are always formed by two of the 

 three angles in turn, whilst the dark line regularly passing from side to side 

 marks the third angle and shows that the filament has a spiral twisting in 

 about 16 joints. On examining the filament where the dark Une touches the 

 margin, if we first raise and then depress the lens, both angles at the point of 

 apparent contact may be distinctly seen. 



The joints are in the front view somewhat quadrangular, broader than long, 

 and each angle has two minute, slightly angidar teeth. The notch between 

 the teeth is veiy distinct but not gaping. The joints are connected by a 



