164 BEITLSH DESMIDIACE^E. 



upwardly produced, obtuse. Vertical view triangular, 

 with straight sides, angles obtusely rounded, sometimes 

 a little produced. Cell-wall smooth. 



Zygospore unknown. 



Length 29-42 /* ; breadth 28-33 /* ; breadth of 

 isthmus 12-17 /x. 



E N GLAND. --New Forest, Hants ! 



SCOTLAND. --Bottomend and Heughhead near Aboyne, 

 Aberdeen (Roy $ Bissett). 



Geoc/r. Distribution. Sweden. Servia. Australia. 

 New Zealand (var.). United States. 



In 1896 we described and figured what we then regarded 

 as the zygospore of St. corniculatum (vide W. & (I. S. West, 

 ' New and Int. Fresliw. Alg.' 1896, p. 157, t. 4, f. 37; ' Alg. 

 S. England/ 1897, p. 493). Subsequent investigation showed 

 the zygospore to belong* to St. trachytithophorum, a species of 

 whose existence at that time we were unaware. 



St. corniculatum is a very rare Desmid, but the following 

 variety, although rare, appears to be widely distributed. 



Var. spinigerum West. (PL CXXV, figs. 19-22.) 



St. corniculatum var. spinigerum West, Alg-. W. Ireland, 1892, p. 171, t. 22, 

 f. 12 ; W. & G. S. West, Alg. N. Ireland, 1902, p. 45, t. 2, f. 22 [forma 

 minor] ; GK S. West, Alg. Yan Yean, 1909, pp. 15, 27. 



Cells smaller, sometimes proportionately a little 

 longer, angles of semicells produced to a variable 

 degree and eacli furnished with a minute spine. 



Length (without spines) 21-28 /i ; breadth 15-25 p. ; 

 breadth of isthmus 9'5-11'5/x,; length of spines T5- 



17 fJL. 



SCOTLAND.- -Rhiconich, Sutherland ! Harris, Outer 

 Hebrides ! 



IRELAND.- -Lough Anna, Donegal (forma minor) ! 

 Lakes between Clifden and Roundstone, Galway ! 



Geor/r. Distribution. Australia. 



Another variety of St . corniculatum described by Xordstedt 

 from New Zealand as "var. rariabilr " (cf. Nordst. 'Fresliw. 

 Alg. N. Zeal/ 1888, p. 39, t. 4, f. 17), sometimes possesses a 

 minute spine at one or more of the angles, which are also 

 more acute. 



