7-> HIMTISH DESMIDIACE.E. 



St. erasum \* distinguished from St. Brebissonii by its more 

 numerous and usually shorter spines, and it also differs in the 

 shape !' its semicells. the apex being almost flat, and the semi- 

 cells widest ill this region. 



Staurastrum erostellum W. & G. S. West. 

 (PL CXXXVT, fig. 12.) 



-/. rostellum var. crostdlntn West & G. S. West, Alg. S. England, 1897, 



P. 4 .:}. t. ii, t. 18. 

 St. erostellum \V. & G. S. West, Notes Alg. II, 1900, p. 296. 



Cells small, about as long as broad, deeply constricted, 

 sinus acute angled and widely open ; semicells inverted 

 subreniform, apex nearly straight or slightly convex ; 

 ll-wnll covered with short stout spines arranged in 

 concentric series around the angles, and rather longer 

 ;it the angles than elsewhere. Vertical view triangular, 

 lateral margins slightly concave, angles somewhat 

 rounded. 



Zygospore unknown . 



Length, without spines, 19*5 [JL ; breadth, without 

 -pines. l ( .)'5(ji. ; breadth of isthmus 6*5 [JL. 



KXGLA:NI>. -Thursley Common, Surrey ! 



Sf. ifnsirUmn differs from St. cosmospinosum (Borg.) W. & 

 G. S. West (=St. rostcllum Roy & Biss.) in its smaller size, its 

 d'-]MT constriction and different form of the semicells, in the 

 :d>sriic' of the large spine at the angles of the semicells, and also 

 in the triangular vertical view with more rounded angles. 



The relative size, number, and arrangement of the smaller 

 -I'liirs is the same as in St. cosmospinosum, although in the 

 latter -|>.-ries they do not increase in size towards the angles. 



Kriteh ( Krrslnv. Alg. Madagascar,' 1914, p. 51) has suggested 

 that this species may be a form of St. clavifertim W. & G. S. West 



Sorth American Desm.' 1895, p. 259, t. 16, f. 25). In this 

 ., however, the shape of the cell is quite different. 



