STAURASTRUM. 107 



Var. evolutum W. G. S. West. (PL CXLV, figs. 



7,8.) 



St. tetracerum var. evolutum West & G. S. West, Freshw. AK Orkneys & 



Shetlands, 1905, p. 25, t, 2, f. 31. 

 St. paradoxum var. G. S. West in manuscript. 



Cells very small, about 1^ times longer than broad, 

 excluding the processes, with a minute excavation at 

 the sinus ; processes long, diverging and often curved ; 

 in vertical view triangular, sides distinctly convex, 

 angles produced into long processes. 



Length, without processes, 10-11 (i ; with processes, 

 27-40 (JL ; breadth, without processes, 7 '5-9 '5 \L \ with 

 processes, 26-50 \L ; breadth of isthmus 4*5 JJL. 



SCOTLAND.- -In the plankton, Shetlands ! 



This variety is distinguished from var. longipes Xordst. by its 

 much smaller size, and its semicells of different proportions, as 

 well as by its convex sides in the vertical view. The latter 

 character and the longer processes readily distinguish it also 

 from var. parvum West. The length of the processes is subject 

 to considerable variation, and the cells are invariably twisted 

 so that the angles of the one semicell alternate with those of 

 the other. 



113. Staurastrum pseudopelagicum W. & G-. S. West. 



(PL CXLV, figs. 11, 12.) 



St. paeudopdarjicum West & G. S. West, Scott. Freshw. Plankton, I, 1903, 

 p. 547, t. 18, f. 1-3 ; Further Contrib. Freshw. Phytoplank. Scott. Lochs, 



1905, p. 504 ; Freshw. Alg. Orkneys & Shetlands, 1905, p. 27. 

 St.pseudopelaqicum VSLT. bifurcation Huitfeldt-Kaas, Plankton Xorske Vande, 



1906, p. 154, t. 2, f. 34, 35. 



Cells rather under medium size, about Ij times 

 broader than long, including the processes, deeply con- 

 stricted ; sinus open, acuminate at its apex ; semicells 

 obversely semicircular, apex only very slightly convex, 

 angles produced to form short, stout, diverging processes 

 tipped with 2 strong diverging spines ; cell- wall rough 

 with granules arranged in concentric series round the 

 processes ; vertical view triangular, sides slightly con- 



