32 BRITISH DESMIDIACE^E. 



each basal angle, which projects over the edge of the 

 sinus. Side view of semicell elongate-pyramidate, 

 angles at base submamillate, lower part of sides convex, 

 upper part of sides concave ; with a dilated apex, the 

 angles of which are bluntly mamillate and upwardly 

 directed. Vertical view oblong-rectangular, with a 

 conical-mamillate protuberance in the middle of each 

 truncate pole, lateral margins retuse in the centre; 

 polar lobe in the form of an oblique cross, the four 

 processes of which are mamilliform. Cell-wall scrobi- 

 culate, scrobiculations larger at all the angles, the 

 surfaces of which become rough (sometimes almost 

 papillate). 



Zygospore unknown. 



Length 108-135 ft; breadth 57-70 p ; breadth of 

 apex 29-37 /u ; breadth of isthmus 13-15'5ju; thick- 

 ness 32-36 fi. 



ENGLAND. Cumberland ! Westmoreland ! (Ralfi). 

 Lancashire ! TT. and X. Yorks ! Surrey ! Hants. 

 (Rolfs). Devon ! (Bennett). 



WALES. Common in Carnarvonshire (up to 2,200 ft. 

 on Glyder Fach) and Merioneth ! 



SCOTLAND. Sutherland !, Ross, Inverness !, Banff, 

 Aberdeen !, Kincardine, Forfar !, Perth !, Argyll, Arran 

 (Roy $' Bissett). Harris and Lewis, Outer Hebrides ! 



IRELAND. Glen Caragh, Cromagloun, and Tore Mt., 

 Kerry ! Pool near Louo'li Glentornan, Donegal ! 



v O O 



Dublin and Wicklow (Archer). 



Geogr. Distribution. France. Germany. Austria 

 and Galicia. Hungary. Norway. Sweden. Finland. 

 Poland. Faeroes. United States. 



This species is often abundant in mountain bogs and the 

 boggy margins of mountain tarns, in which situations it is 

 commonly found amongst the leaves of a submerged form of 

 Sphagnum cuspidatum. It exhibits considerable variation in 

 the leno'th of the "neck " and in the form of the basal ano'les 



O O 



of the semicells. These variations are connected by every 

 intermediate state, so that it is impossible to clearly define 

 such forms as " var. montanum E/acib." or "var. elegans 

 Schmidle." The Desmid described and figured by Wolle 



