210 BRITISH DESMIDIACE.E. 



Mitcham Common, Surrey ! Sussex arid Kent (Ralfs). 

 Dartmoor, Devon (Harris). Cornwall ! (Ralfs). 



WALES. Capel Curig ! (Cooke & Wills) and Glyder 

 Fawr (Roy), Carnarvonshire. Dolgelly, Merioneth (Ralfs). 

 In the plankton ! 



SCOTLAND. --Aberdeen, Kincardine, Forfar, Perth (Roy 

 & Biss.). Shetlands ! Not uncommon in the plankton ! 

 Plankton of Loch Gorma, Inverness ; and of Loch 

 Diracleet, Harris, Outer Hebrides ! 



IRELAND.- -In the plankton, Mayo ! Derryclare Lough, 

 Ballynahinch, and in the plankton, Galway ! Lough 

 Guitane and in the plankton, Kerry ! 



Geogr. Distribution. --Fiance. Belgium. Germany. 

 Switzerland. Galicia in Austria. Hungary. Italy. 

 Turkey. Norway. Sweden. Denmark. Bornholm. 

 Finland. N. and S. Russia. Faeroes. India. United 

 States. Patagonia. 



Forma minor West. (PL CLIX, fig. 12.) 



Sph. vertebratum f. minor West, Add. Alg. W. Yorks. II, 1891, p. 244 ; 

 Alg. Engl. Lake Distr. 1892, p. 6, t. 9, f. 3. 



Differs from the type in its smaller size, its relatively 

 broader isthmus, and somewhat more depressed cells. 



Length 8-10 u. ; breadth 12-14 \L ; breadth of isthmus 

 7-5-8(1. 



ENGLAND.- -Harrop Tarn, Cumberland ! Brother's 

 Water, Rydal Fell, and Stickle Tarn, Westmoreland ! 

 Malham Tarn, W. Yorks ! 



Var. punctulatum W. & G. S. West. (PL CLX, fig. 12.) 



Sph. punctulatum West, Alg. Maine, 1891, p. 1, t. 315, f. 1, 2. 

 Sph. vertebratum var. punctulatum West & G. S. West, Freshw. Alg. Orkneys 

 & Shetlands, 1905, p. 28 ; Phytoplankton Engl. Lake Distr. 1909, p. 290. 



Cells more angular than in the type, and distinctly 

 punctate. 



Length 14-16 [JL; breadth 17'o-20p; thickness 10 pi; 

 breadth of isthmus 8-9 '5 . 



