210 BRITISH DESMTDIACE/K. 



Alc;a-fl. Cambr. 1899, p. 113 ; West & G. S. West, Al^a-fl. Yorks. 1900, 

 1>. 58; Freshw. Chlorophy. Koli Chang, 1901, p. 1<>7 ; Alf. N. Ireland, 

 I ( .nc', p. 20. 



Dori'iiinii T>-<iln'''i<la Eeinsch, Algonfl. Frank. ISOT.p. 1S3 (in part) ; Wowt. 

 Itrsin. Mass. 1SS9, p. 17, t. 2, f. 11 ; Turn. Frosluv. AU;-. E. India, 1893, 

 p. 3S ; L'oy & Uiss. Scott. Desm. 1894, p. 242. 



Cells large, subcylindrical, 11-15 times longer than 

 their diameter; semicells with one basal inflation, 

 rarely with a second slight undulation above it, almost 

 cylindrical, gradually attenuated towards tin- apices. 

 lateral margins almost straight, generally faintly 

 convex ; apices rounded-truncate, destitute of tubercles; 

 cell-wall punctate. 



Zygospore ellipsoid and smooth. 



Length 390-664 /A; breadth at base of semicells 

 26-46 /A; breadth of apices 16-32/x; length of /ygosp. 

 70 /x, breadth 48 p. 



ENGLAND. Cumberland ! Westmoreland ! (.///W//). 

 W. and N. Yorks ! Lancashire! Essex! Cambridge ! 

 Surrey ! Hants ! Devon ! Cornwall ! 



WALES. Capel Curig and Glyder Fawr (at 2,700 ft.), 

 Carnarvonshire ! 



SCOTLAND. Sutherland ! Ross ! , Inverness, Aber- 

 deen ! , Kincardine, Perth ! , Arran (Hoi/ <$ ///.s.sv//). 

 ( 'umbrae, Ayr ! Lewis, Outer Hebrides ! Orkneys ! 



II.'KLAND. Donegal! Galway ! Kerry! 



(Irot/r. Distribution. France. Germany. Austria 

 and Galicia, Italy. Norway. Sweden. Denmark. 

 N., Central, and S. Russia, Iceland (var.). Nova 

 Zembla. Greenland. Central China (var.). Japan 

 (var.). India. Siam. Singapore. Abyssinia, Aus- 

 tralia (var.). United States. Brazil. Argentina. 

 Uruguay. 



Cl. Trahecula Ehronb. appears to linvo hoon a composite 

 s])(H-ics as is amply illustrated on tab. 6 of Ehrenberg's 

 f Inf usionsthierchen/ 1S:',S, f. II 1-7. From tlu-so lignrcs 

 recent- authors have selected the two (fi^'s. 114 and 117) 

 wliieli most nearly a^ree with the widely distributed type of 

 Plewrotsenium descrilied ultove. 



It seems generally recognised that Pleurotaenium Trabecula 

 is a moderately large species, with one basal inflation to tin- 



