190 BRITISH DESMLDIACE.E. 



towards the centre, where there is a small ill-defined 

 clear space surrounding a pair of closely adjacent 

 tumours ; central tumours rather small and covered 

 with large irregularly arranged granules, those of 

 one tumour merging with those of the other. Side 

 view of semicell ovate, with a rounded apex and a 

 granulate inflation on each side near the base. Verti- 

 cal view rather narrowly elliptic, with a pair of 

 adjacent granulate tumours at the middle on each side. 

 Chloroplasts axile, with two pyrenoids. 



Zygospore unknown. 



Length 60-77 n; breadth 50-6 7 p.; breadth of apex 

 21 '5-25 /A; breadth of isthmus 14-20 ^ ; thickness 

 29-38 p. 



ENGLAND. Borrowdale and near Cockermouth, 

 Cumberland ! Westmoreland ! Lancashire ! W. and 

 N. Yorks ! Leicestershire (Roy). Lincolnshire! 

 Norfolk ! Cambridgeshire ! Warwickshire ! Surrey ! 

 Hants ! Devon ! Cornwall ! 



WALES.- -Llyn Cwlyd !, Glyder Fawr (Roy), and 

 near Bettws-y-Coed !, Carnarvonshire. Dolgelly, 

 Merioneth ! 



SCOTLAND.- -Coul and Loch Kinnellan, Ross; Sand 

 Loch, Collieston, Howford, Inverurie, and Glen Cairn, 

 Aberdeen ; Rannoch, Perth ; near Kingshouse, Argyll 

 (Roy fy Bissett). Plankton of Loch Asta, Shetlands ! 



IRELAND.- -Donegal ! Mayo ! Kerry ! Wicklow ! 

 Londonderry ! Armagh ! In the lake-plankton of 

 Kerry ! Plankton of Lough Neagh and Lough Beg ! 



Geocir. Distribution. France. Germany. Austria. 



' / 



Poland. Hungary. Italv. Norway. Sweden. 



O e/ */ .' 



Bornholm. Finland. N. Russia (var.). Iceland. 

 Greenland. Nova Zembla. Siberia. India. United 

 States. Brazil (form). Ecuador. Argentina. 



C. Tnrj_n'uii is a very characteristic species with a wide 

 distribution in the British Islands. It is not a bog-species, 

 but occurs chiefly at the weedy margins and in the plankton 

 of large pools and shallow lakes. It thrives amongst Potamo- 

 getons, etc., in the surface waters of the large dykes and 



