STAURA STRUM. I 89 



lateral angles scarcely rounded, furnished with a 

 nmcro (or very minute spine). Vertical view tri- 

 angular, median portion of sides retuse, angles acutely 

 rounded and mucronate. Cell-wall granulate ; granules 



O 7 O 



minute and arranged in concentric rinses around the 



o o 



angles, much reduced and scattered at each apex. 



Zygospore globose, furnished with long slender 

 spines, which are slightly furcate at the apex. 



Length 29-33 /i; breadth (with nmcro) 27-33 p.; 

 breadth of isthmus 9-12*5 \L ; diam. zygosp. without 

 spines 32'5-34'5 ju,, with spines 62-65 /x, ; length of 

 spines 13 '4-1 5* 5 /x. 



ENGLAND.- -Epping Forest, Essex ! Near Crowan, 

 Cornwall (with zygospores) ! 



WALES.- -Capel Curig !, and Grlyder Fawr (Roy), 

 Carnarvon shire. 



SCOTLAND.- -Rhiconich, Sutherland ! Near Tain, 

 Ross ; Birsemore, Aberdeen ; Cammie, Heughhead 

 and Dalbrake (with zygospores) in Strachan, Kin- 

 cardine (Eoij $ Bissett). Plankton of lakes in Lewis, 

 N. Uist, and Benbecula, Outer Hebrides ! Shetlands ! 



IRELAND.- -Loughs Cloncarney and Grartan, Donegal ! 

 Derryclare Lough, Galway ! Plankton of Lough 

 Neagh ! Lough Fea and Plankton of L. Beg, Lon- 

 donderry ! 



Gfeogr. Distribution.- -France. Germany. Galicia 

 in Austria. 



St. granulosum is at once distinguished from all forms of 

 St. punctulatum by the more flattened apices of the semicells 

 and the mucronate angles. The cells are slightly variable in 

 external form, due largely to differences in proportionate 

 length and breadth. 



We Lave previously mentioned (' Joura. Bot.' 1903, p. 76) 

 that the figure of the zygospore given by Roy and Bissett is 

 very indistinct and specifically unrecognizable. 



Forma connexa. (PI. CXXVIII, fig. 13.) 



Angles of semicells furnished with a pair of minute 

 spines in place of a single mucro. 



