144 BRITISH DESMIDIACE-1-:. 



rounded and mamillate. Cell-wall delicately punctate- 

 scrobicnlate. 



Zygospore unknown. 



Length 83-103 p.; breadth 111-134 /x ; breadth of 

 isthmus 21-27 /x. 



SCOTLAND.- -In the plankton of Loch Shin and Loch 

 Grhriama ; also in a small pool at Rhiconich, Suther- 

 land ! 



One of the largest and most striking species of the genus, 

 St. conspicuum can be compared with St. majusculum Wolle, 

 from which it differs in the form of its semicells,, its sinus, 

 and the form of the vertical view. From St. grande it is at 

 once distinguished by the entirely different sinus, the 

 shape of its semicells, and the mamillate angles. 



13. Staurastrum aversum Lund. 

 (PL CXX, figs. 9-13.) 



Staurastrum aversum Lund. Desm. Suec. 1871, p. 59, t. 3, f. 27 ; Cooke in 

 Journ. Quekett Micr. Club, 1881, p. 206, t. 16, f. 36; Brit. Desm. 1887, 

 p. 166, t. 55, f . 6 ; De Toni, Syll. Alg. 1889, p. 1202 ; West, Alg. N. 

 Wales, 1890, p. 294; Eoy & Biss. Scott. Desm. 1893, p. 178; Nordst. 

 Index Desm. 1896, p. 54 ; W. & G. S. West, Notes Alg. Ill, 1903, p. 75 ; 

 Scott. Freshw. Plankton, I. 1903, p. 529; Further Contrib. Freshw. 

 Plankton Scott. Lochs, 1905, p. 486 ; Comp. Study Plankton Irish 

 Lakes, 1906, p. 86 ; Brit. Freshw. Phytoplankton, etc., 1909, p. 181. 



Cells of medium size, about 1J times as long as 

 broad, deeply constricted, sinus acute-angled and 

 widely open ; semicells obversely elliptic-semicircular, 

 apex truncate or slightly retuse (rarely convex), 

 ventral margin very strongly convex, angles broadly 

 rounded, each furnished with a minute papilla. 

 Vertical view triangular, with broadly rounded angles 

 and slightly concave sides, each angle furnished with 

 a minute papilla. Cell- wall very delicately punctate. 



Zygospore unknown. 



Length 35-58 ^ ; breadth 29-45 p. ; breadth of 

 isthmus 10-17 /x. 



WALES.- -Capel Curig! (Cooke fy Wills), near Llan- 

 fairfechan, and Llyn-y-cwm-ffynon, Carnarvonshire ! 

 Plankton of several of the Welsh lakes ! 



