134 BRITISH DESMIDIACE^. 



processes. It may also be compared with. St. foliatum Turn., 

 but Turner's figure is too indistinct to admit of a detailed 

 comparison. 



Var. subcontortum W. & G. S. West. (PL CL, fig. 12.) 



St. margaritaceum var. subcontortum West & G. S. West, Alg. S. England. 

 1897, p. 496, t. 17, f. 15-17. 



Cells in vertical view 6- or 7-radiate ; processes trun- 

 cate and all curved in one direction as in St. cyrtocerum. 

 Length 26 [i ; breadth 25-27 [i ; breadth of isthmus 



9(1. 



ENGLAND.- -Devil's Jumps, Frensham, Surrey ! 



* 



134. Staurastrum Chavesii Bohlin. 

 (PL CXLIX, fig. 12 ; PL CLXVI, fig. 1.) 



Staurastrum Chavesii Bohlin, Flor. Algol, d'eau douce d'A5ores, 1901. p. 56, 



f. 15. 

 ? St. subtile Schmidle, Beitr. Alp. Alg. 1895, p. 37, t. 16, f. 12. 



Cells small, about as long as broad, or up to 1^ times 

 broader than long, including the processes ; constriction 

 fairly deep, sinus rounded, almost semicircular ; semi- 

 cells inversely subtrapeziform, apex straight or slightly 

 concave ; upper angles of the semicell produced to form 

 short stout diverging processes, biundulate and denticu- 

 late, truncate at the apex, and with 4 tiny apical spines ; 

 lateral margins of semicell with conspicuous emarginate 

 protuberances at the point of origin of the processes. 

 Vertical view quadrangular, sides concave, angles pro- 

 duced into short nodulose processes ; apex with an 

 emarginate projection at the base of each process. 



Zygospore unknown. 



Length 10-17 pt ; breadth, including processes, 15-22^ ; 

 breadth of isthmus 6 '5-8 JJL. 



IRELAND. --Near Ballynahinch, Galway ! 



Geogr. Distribution. Austria . Azores . 



The distinctive characters of this species are the obtuse sinus 

 and the four emarginate processes on the dorsal surface, one at 



