DESMIDIUM. 247 



Filaments triangular, twisted, usually destitute of a 

 conspicuous gelatinous sheath ; cells large, about 2J 

 times broader than long, constriction moderately deep, 

 sinus linear towards its apex, opening more widely ; 

 semicells narrowly oblong, lateral margins usually 

 somewhat obliquely truncate, with the upper angle of 

 the truncate margin conspicuously protruded towards 

 the apex of the semicell, the lower angle more rounded ; 

 apex of semicell broadly truncate, with a short connect- 

 ing process at each angle of the cell ; middle of apex 

 very slightly concave ; spaces between the cells not 

 visible, or recognised only with difficulty ; vertical view 

 triangular, angles acutely rounded, sides slightly con- 

 cave ; chloroplasts axile, one in each semicell, witli 

 two massive lobes radiating from the centre into each 

 angle of the semicell, and a large pyrenoid opposite each 

 face. 



( Zygospores smooth and oval. 



Length 1 2-20 pi ; breadth 37-50 JJL ; breadth of 

 isthmus 30-42-5 [/. ; breadth of apices 30-41 \L ; length 

 of zygospore 28-36 p ; breadth 20-28 (i. 



ENGLAND. Cumberland ! Westmoreland, at 2400 ft. 

 on Helvellyn. and in the plankton of Grasmere ! Lan- 

 cashire ! (Rolfs). W. and N. Yorks ! Essex (Hassall). 

 Warwick's! (Wills). Berks (Griffiths). Surrey! Sussex 

 (Ralfs). Hants ! (Bein/cff). Dartmoor, Devon (Harris) 

 Cornwall ! 



WALES. Capel Curig !, Llyn Idwal !, and in the 

 plankton !, Carnarvonshire. Llyn Coron, Anglesea ! 

 Dolgelly, Merioneth (Ralfs). Swansea, Glamorgan 



(Ralfs). 



SCOTLAND. General ; zygospores at Tomacher, 

 Aberdeen (Roy & Biss.). In the plankton ! Bute ! 

 Harris, Outer Hebrides ! 



IRELAND. - -Donegal ! Mayo! Gal way ! Kerry! 

 Dublin and Wicklow (Arch.). Meath (Ralfs). 



Geogr. Distribution.- -France. Germany. Switzer- 

 land. Galicia and Austria. Hungary. Servia. Eon- 

 mania. Turkey. Italy. Spain. Portugal. Norway. 



