90 BRITISH DESMIDIACE^E. 



Norway. Sweden. Denmark. Finland. Faeroes. 



t> 



W. Greenland. Japan. Australia. Azores. United 

 States. Guiana (var.). Colombia. 



St. brachiatum is a frequent inhabitant of Sphagnum bogs, 

 and is sometimes obtained in abundance from such localities. 

 It is often found in plankton, but never occurs in great numbers 

 in this habitat. It is one of the most variable of Desmids, 

 particularly with regard to the relative length and stoutness of 

 the processes and the character of their apices. The processes 

 may be fairly long and slender, or sometimes quite short and 

 stout, whilst their apices may be 2- or 3-fid, both types occurring 

 occasionally in the same individual ; or the ultimate divisions 

 may be bluntly rounded, and in extreme cases wanting alto- 

 gether. The semicells are frequently twisted so that corre- 

 sponding angles do not overlie each other. 



107. Staurastrum laevispinum Bissett. 

 (PL CXLI, figs. 17, 18.) 



SV. loecispinum Biss. Desm. Winder-mere, 1884, p. 195, t. 5, f. 5 ; Cooke, 

 Brit, Desm. 1887, p. 143, t. 50, f . 3 ; De Toni, Syll. Alg. 1889, p. 1144 ; 

 Roy & Biss. Scott, Desm. 1893, p. 22 ; West & G. S. West, Alg. N 

 Ireland, 1902, p. 49, t. 2, f. 37 ; Brit. Freshw. Phytoplankton, 1909, p. 202. 



Cells small, sinus obtuse and nearly rectangular, with 

 a minute excavation at its apex ; semicells somewhat 

 lunate, angles produced into thick, slightly divergent 

 processes, which are slightly attenuated towards their 

 obtuse apices ; apex of semicell concave. Vertical view 

 triangular, sides concave, angles produced and tapering. 



Zygospore unknown. 



Length 25-30 p ; breadtli 32-39 p ; breadth of isth- 

 mus 9 [L . 



ENGLAND.- -Xear Bowness, Westmoreland (Biss.). 

 Dartmoor, Devon (Harris). 



SCOTLAND. Goat Fell, Arran (Roy & Biss.). Plank- 

 ton of Loch nan Eun, N. Uist, Outer Hebrides ! 



IRELAND.- -E. of Glenties ; Lough Anna and Sproules 

 Lough, Donegal (form) ! 



Geogr. Distribution. Australia (form). 



