142 EEITISH DESMIDIACE^l. 



running from base to apex of each semicell, each band 

 with several rather small pyrenoids. 



Zygospore unknown. 



Length 11 2-120 ft; breadth 95-104 /A; breadth of 

 isthmus 21-25 p.; thickness 50 //,. 



ENGLAND. Cumberland! Westmoreland! (Bissett). 

 W. and IN". Yorks ! Lancashire! Norfolk (CooJce). 

 Warwick (Wills). Surrey! Sussex (Ralfs). Kent 

 (Ralfs). Hants! (Rolfs). Devon I (Bennett). 



WALES. General in Carnarvonshire (up to 2,700ft. 

 on Grlyder Fawr) ! Dolgelly and Ffestiniog, Merioneth ! 

 Llyn Coron, Anglesey ! 



SCOTLAND.- -Sutherland ! , Ross, Inverness ! , Aber- 

 deen, Kincardine, Forfar, Perth ! , Argyll, Arran (Roy 

 fy Bissett). Outer Hebrides ! Orkneys ! 



IRELAND.- -Widely distributed in Donegal, Galway, 

 and Kerry ! Mayo ! Dublin and Wicklow (Archer). 



Geogr. Distribution.- -France. Belgium. Germany. 

 Galicia in Austria. Hungary. Norway. Sweden. KT. 

 Russia. Poland. Azores (var.). United States. 



This characteristic species is widely distributed in the 

 upland districts of the British Islands, and often occurs in 

 abundance among submerged Sphagnum. It is frequently 

 associated with Cosmarium Cucurbita, Euastrum insigne, 

 Micrasterias oscitans var. mucronata, M. truncata, Gymnozyga 

 moniliformis, Tetmemorus granulates, and Netrium Digitus. 



It is characterized by its pyramidate-semicircular semicells 

 with a rounded apex, by its deep constriction, and by the 

 parietal chloroplasts. The cell-wall is generally finely punc- 

 tate, hut may be delicately scrobiculate, and old individuals 

 often become quite asperulate on the exterior. 



Wolle gives a minimum length of 70 /UL and a minimum 

 breadth of 60 fj. for his American specimens, but we have not 

 seen any British forms so small as this. 



Var. montanum Racib. (PI. LVIII, fig. 3.) 



Cosmarium Ralfsii var. montanum Racib. Norm. Desin. Polon. 1885, p. 70, 



t, 10, f. 4 ; West, Alg. W. Ireland, 1892, p. 163. 

 Pleurotseniopsis Ralfsii var. montana (Racib.) De Toni, Syll. Alg. 1889, 



p. 911. 



Cells with the sinus opening outwards, basal angles 

 of semicells less rounded and slightly produced. 



