STAURASTRUM. 27 



Cells small, about 1| times longer than broad, deeply 

 constricted, sinus obtuse, nearly semicircular ; semicells 

 relatively more broadly oval than in St. cuspidatum, 

 each angle terminated by a short spine. End view tri- 

 angular, sides concave, angles slightly inflated, and ter- 

 minated by a short spine. Cell-wall minutely punctate. 



Zygospore unknown. 



Length, without spines, 20-35 pt ; breadth, without 

 spines, 14-27 [j. ; breadth of isthmus, 4-7 fji ; length of 

 spines, 4-6 \i. 



WALES. Capel Curig, Carnarvonshire ! 



Geogr. Distribution. Japan. Madagascar. 



This species is distinguished from the preceding one by its 

 relatively stouter and more broadly oval semicells. The spines 

 are usually parallel, or sometimes very slightly incurved or di- 



vergent. 



56. Staurastrum leptodermum Lund. 

 (PL CXXXII, fig. 20.) 



Staurastrum leptodentnutt Lund. Desm. Suec. 1871, p. 58, t. 3, f. 20; De 

 Toni, Syll. Alg. 1889, p. 1144 ; Roy & Biss. Scott, Desm. 1894, p. 22 ; 

 West & G. S. West, Wehv. Afric. Freshw. Alg. 1897, p. 45 (forma) ; 

 Liitkem. Desm. Central China, 1900, p. 123, t, 0, f. 30, 31 (forma). 



Cells of medium size, about as long as broad, deeply 

 constricted, sinus broad and subrectangular ; semicells 

 cuneate, widening considerably towards the apex, sides 

 nearly straight, but with two obscure undulations, apex 

 slightly tumid in the middle, angles terminating in a 

 minute spine directed c L liquely upwards. Vertical 

 view triangular, sides straight, angles acute with a 

 short spine. Cell-wall very thin ; chloroplast axile. 



Zygospore unknown. 



Length 58-60 p. ; breadth, without spines, = length ; 

 breadth, with spines, 61-64 ^ ; breadth of isthmus 22 pi. 



SCOTLAND. Slewdrum, Aberdeen (Roy d' Biss.). 



Geogr. Distribution. Sweden. Finland. Central 

 China. Bengal. 



