STAURASTRITM. 169 



near the shore of Lake Xyasa in Central Africa (Consult 

 G. S. West, < Alg. Third Tanganyika Expedit.' 1907, p. ]25) ; 

 this was named " forma minor" ; length 28 in ; breadth 25 fj 

 breadth of isthmus 10 ju. 



Var. arcticum \Ville. (PI. CXXVII, fig. 24.) 



St. turgescens var. arcticum "\Ville. Ferskv Alg. Xov. Semlj. 1879, p. 51, 

 t. 13, f. 57 ; W. & G. S. West, Alga-fl. York*. 1901, p. J02. 



Cells proportionately narrower, sinus a little more 

 open ; semicells very broadly elliptic (almost rotund- 

 elliptic) ; sides of vertical view convex. 



Length 45 ^ ; breadth 30 JJL ; breadth of isthmus 



/i. 



ENGLAND. Ogden Clough, W. Yorks ! 

 . Distribution.- -Novs, Zembla. 



30. Staurastrum Donardense \V. & G. S. West. 



(PI. CXXVI, fig. 7.) 



Staurastrum Donardense W. & G. S. West, Alg. X. Ireland, 1902, p. 50, 

 t. 2, f. 33. 



Cells small, a little longer than broad, deeply con- 

 stricted, sinus narrowly linear with a faintly dilated 

 extremity ; semicells elliptic-semicircular, basal angles 

 broadly rounded, apex subtruncate in the middle. 

 Vertical view triangular, angles broadly rounded, sides 



o o / 



straight or very slightly concave. Cell-wall very 

 minutely granulate, granules arranged in indistinct 

 rings around the basal angles. 



Zvgospore unknown. 



Length 25'5-27 /* ; breadth 21-23 /i; breadth of 

 isthmus G'5-7'5 /LL. 



IRELAND.- -Slieve Donard (abundant at 1800 ft.) and 

 Slievecommedagh (at 2000 ft.), Down ! 



This species occurred abundantly amongst numerous ex- 

 amples of St. turgescens in boggy pools on granitic rocks. 



It should be compared with St. smaragdinum Turn. 

 ('Freshw. Alg. of E. India/ 1893, p. 103, t, 13, f. 14) from 

 which it differs in its more rounded semicells with natter 

 apices, its coarser granulation, its wider isthmus,, and in the 



