BRITISH DESMIDIE.E. 57 



that takes place, for they become more widely separated, and then 

 the new teeth appear, very minute at first, but gradually enlarging, 

 until the new segment equals the older one in breadth. 



1. D. Grevina (Kntz.) ; sheath distinct ; joints of the filament broader 

 than long, with a thickened border at their junction ; transverse 

 view broadly elliptic. 



Desmidium cyUndricum, Greville, Scot. Crypt. Fl. t. 293. (1827) ; in Hook. 



Brit. Fl. V. 2. p. 402. Ag. Consp. Biatom. p. 56. Kutzing, Synop. 



Diatom, in LimiiEa 1833, p. 614. Brebisson, Alg. Fed. p. 64. Harv. 



Brit. Alg. p. 197. Menegh. Syyiop. Desmid. in LinncBa 1844, p. 204. 



Ralfs, Annals of Nat. Hist. v. 11. p. 373. t. 8. f. 1 ; Trans. ofBot. So- 

 ciety of Edinburgh, v. 2. p. 6. t. 2. Hassall, Brit. Freshwater Algce, 



p. 342. t. 83. f. 1. 

 Arthrodesnius? cylindricus, Ehr. Infus. p. 142 (1838). 

 Hyalotheca cylindrica, Ehr. Kurze Nachricht iiber 27 A seit dem Abschluss 



der Tafeln des grossern Infus. neu beobachtete Infus. (1840). 

 Desmidium compressum, Corda, Obser. micros, sur les Anim. de Carlsbad, 



p. 18 (1840). 

 Didymoprium Grevillii, Kiitzing, Phycologia Generalis, p. 166 (1843) ; 



Phy. Germ. p. 141. 

 Didymoprium cyUndricum, Ralfs, Annals of Nat. Hist. v. 16. p. 10 (1845) ; 



Trans, of Bot. Soc. of Edinburgh, v. 2. p. 164. 

 Hyalotheca Grevillii, Brebisson in lit. (1846). 



Appin, Capt. Carmichael. Dolgelley ; Carnarvon ; Penzance, &c., /. R. 

 Chiltington Common near Pulborough, and Ashdown Forest, Sussex ; near 

 Southampton, Hants, and Reigate, Surrey, Mr. Jenner. Clieshunt, Mr. Has- 

 sall. Meath, Mr. Moore. Aberdeenshire, Dr. Dickie and Mr. P. Grant. 

 Manchester, Mr. Williamson. Ambleside, Mr. Sidebotham. 



Prussia, Kutzing. Prague ; Carlsbad ; Reichenberg, &c., Corda. Falaise, 

 Bribisson. New York ; Rhodes Island, Bailey. 



The filaments in Didymoprium Grevillii are as thick as those of Desmidium 

 Swartzii, which in water is a very similar plant, and are very gelatinous and 

 fragile ; their colour is pale green, but, except when very young, somewhat 

 opake. The joints are connected by a thickened border, and, inclusive of the 

 angles, which are colourless, are rather broader than long, and oval ; the angles 

 are bidentate, their teeth angular. When the angles are not\-isible the joints 

 are nearly quadrate. 



The mucous sheath is very e\'ident, narrower in this plant than in Hyalo- 

 theca dissiliens, and waved at the margin. "When the angles are not visible 

 the undulation of the margin is slight, but becomes more marked as the angles 

 become visible. The sheath is jointed as well as the filament, the lines of 

 separation being sometimes distinctly apparent. 



The filaments are regularly twisted, and at about every tenth joint the 

 angles become very perceptible, whilst in the two central joints thej^ are almost 

 invisible ; on slightly altering the position of the filament the angles in the 

 latter become visible, and in the former chsappear. 



