74 BRITISH DESMIDIACE^E. 



Xorway. Sweden. Austria. Huno-ary. Russia. 



t O v f 



Lapland. Faeroes. Greenland. Ceylon. Singapore. 

 lava. Central China. Xew Zealand. Brazil. 



Tins is a well-marked species with tlie aspect of a strain-lit 

 Closterium. Forms are sometimes met with in which there 

 are two thickened bands round the centre of the cells ; we give 

 a h'o-ure of one of these forms from Capel Curio-, X. Wales 

 (PL Til, fig'. 8). Gutwinski has described this form as 

 Clnxii-r/Hin Tfctiiiii (r/Ve Gutw. Nonn. Ala; 1 . Nov. 1896, p. 35, 

 t. v, f. 3). 



Liitkemuller is probably correct in considering- Peniniii 

 LibfUnla as a true species of Closterium. It is in a case of this 

 kind that the distinction between Penium and Closterium com- 

 pletely breaks down. 



Yar. interruption West & G. S. West, (PL VII, figs. 



9, 10.) 



Penium closterioides forma interrupta West, Alg. Eng. Lake Distr. 1892, 

 p. 721 ; Schmidle, Beitr. Alg. Schwarzwalcl. 1893, p. 88, t. 3, f. 7. 



P. Libellula var. interruptum West & G. S. West, Alg. S. England, 1S97, 

 p. 479 ; Desm. Singapore, 1897, p. 156 ; Freslnv. Alg. Ceylon, 1902, p. 135. 



Somewhat smaller than the typical form, with each 

 chloroplast transversely divided, so that there are four 

 axile chloroplast s in each cell arranged in a longi- 

 tudinal series. 



Length 122-240 /t; breadth 24-44 ju. 



ENGLAND. Black Sail Pass, Cumberland! Lough - 

 risrsr and Elter Water, Westmoreland ! Chobhani 



c^ o 



Common, Surrey ! 



SCOTLAND. Loch Doon, Ayr ! Rhiconich, Sutherland ! 

 Geofjr. Distribution. Germany. Ceylon. Singapore. 



Var. intermedium Roy & Biss. (PL VII, fig. 11.) 



var. intermedium Eoy & Biss. Scott. Desm. 1894, p. 252. 

 West & G. S. West, Desm. Singapore, LS97, p. 156; Alg. N. Ireland, 

 1902, p. 21; Freshw. Alg. Ceylon, 1902, p. 136. 



Rather less than half the size of the typical form, 

 but otherwise precisely similar. 



Length 102-132 /*; breadth 10-20 /*. 



Ex< : i ,.\ x i . Westmoreland ! Surrey ! Cornwall ! 



