46 BRITISH DESMIDIACE^l. 



which are scarcely thickened at the free margin, pyre- 

 noids many. 



Zygospore unknown. 



Length 142-210^; breadth 19-35 /w; breadth of 

 apices lO'o-H'5^. 



IRELAND. Lough Anna, Donegal ! 



Geogr. Distribution. Austria. Germany. 



In the Irish specimens the chloroplast possessed six almost 

 straight ridges, and extended the whole length of the cell 

 with the exception of a very small space at each end. In 

 many specimens the chloroplast was partially interrupted 

 in the middle, and most of the examples appeared to be faintly 

 constricted. The apices were distinctly more truncate than 

 those figured by Lutkemiiller, but Rabeiihorst says " utroque 

 polo truncata," and Lutkemiiller has since remarked that the 

 apices are probably subtruncate. It is a very rare species. 



13. Spirotaenia acuta Hilse. 

 (PL III, figs. 14, 15.) 



Spirotip.nia acuta Hilse, in Rabenh. Alg. 1866, no. 1830 ; Eabenh. Fior. 

 Europ. Alg. Ill, 1868, p. 148 ; Cooke, Brit. Desm. 1887, p. 185, t. 66, 

 f . 5 ; Liitkem. Gatt. Spirotsen. 1895, pp. 56, 93 ; Nordst. Index Desmid. 

 1896, p. 39 ; West & G. S. West, Alga-fl. Yorks. 1900, p. 41 ; Alg. N. 

 Ireland, 1902, p. 19. 



Cells small, (2-|- )5-8 times longer than their dia- 

 meter, fusiform, tapering from the middle to the apices, 

 which are acute ; chloroplast axile, with several (3 or 4) 

 spirally arranged ridges which sometimes anastomose. 

 Pyrenoid usually solitary. 



Zygospore unknown. 



Length 30-37 n ; breadth 6-7 -2 p. 



ENGLAND. Pilmoor, N. Yorks ! Hampsfell, Lanca- 

 shire ! 



SCOTLAND. Upper Powlair, Slewdrum, Culblean, 

 Aberdeen; Den of Garrol and Dalbrake, Kincardine; 

 Fintray Hills, Stirling (Roy fy Bissett). Rhiconich, 

 Sutherland ! Near Balallan, Lewis ; and near Tarbert, 

 Harris, Outer Hebrides ! 



IRELAND. Gal way (Archer). Near Grweedore ; 

 Loughs Anna and Machugh, Donegal ! 



