124 BRITISH DESMIDIACE^E.. 



it easy of distinction. It is nearest to St. pseudotetracerum West, 

 but is much smaller, its processes are shorter and more robust, 

 and the spines at the dilated apices of the processes and two 

 rings of short spines at their base distinguish it. 



128. Staurastrum latiusculum W. & G. S. West. 



(PL CXLIX, fig. 8.) 



Staurastrum latiusculum West & G. S. West. Alg. N. Ireland, 1902, p. 53, 

 t. 1, f. 20. 



Cells small, about li times broader than long, includ- 

 ing the processes, constriction fairly deep, sinus open, 

 broadly semi-elliptical ; semicells inversely trapeziform, 

 apex slightly convex, lower angles rectangular, upper 

 angles produced to form fairly long, distinctly diverging 

 processes, each with three denticulate undulations and 

 tipped with 3 minute spines. Vertical view quadrangular, 

 sides slightly concave, angles produced to form long 

 denticulate processes, with a conspicuous small spine 

 on each side at the base of each process. 



Zygospore unknown. 



Length, without processes, 13[i; with processes, 

 19-23fji ; breadth, without processes, about 13-1 3 'opt ; 

 with processes, 32 \L ; breadth of isthmus 9 (i. 



IRELAND. Near Glenties, Co. Donegal ! 



The distinctive characters of this species are its small size, its 

 relatively broad body with a small semi-elliptical sinus, and the 

 paired spines at the base of each process. 



129. Staurastrum pelagicum W. & G. S. West. 



(PI. CXLVI, fig. 6.) 



Staurastrum pdagicum West & G. S. West, Freshw. Alg. N. Ireland, 1902, 

 p. 46, t. 2, f. 26, 27 ; Comp. Study Plank. Irish Lakes, 1906, p. 86 ; 

 Ostenf. & Wes.-Lund, Fortnightly Explor. Plankton Icelandic Lakes, 

 1906, p. 1111 ; Borge in Botan. Notiser, 1913, p. 49. 



Cells of medium size, 1-g- times broader than long, 

 without the processes, deeply constricted, sinus open, 

 but becoming very narrow towards its apex ; semicells 



