STAURASTRUM. 193 



174. Staurastrum Arctiscon (Ehr.) Lund. 

 (PL CLVII, fig. 5.) 



Xa nth id turn No 2 Bailey, Amer. Bac. 1841, p. 291, t. 1, f. 15. 



Xanthidium Arctiscon Ehr. Micr. Leb. S. u. N. Amer. 1843, p. 138 ; Ralfs, 



Brit. Desm. 1848, p. 212 ; Rabenh. Flor. Europ. Alg. 1868, p. 224 ; 



Kirchn. Alg. Schles. 1878, p. 155. 

 Staurastrum Arctiscon Lund. Desm. Suec. 1871, p. 70, t. 4, f. 8 ; Wills in 



Midi. Nat. 1881, t. 4, f . 5 ; Wolle, Desm. U. S. 1884, p. 148, t. 47, f. 9, 10 ; 



Cooke, Brit. Desm. 1887, p. 179, t. 63, f. 1 ; De Toni, Syll. Alg. 1889, 



p. 1226 ; Roy & Biss. Scott. Desm. 1893, p. 17 ; West & G. S. West, 



.Some N. Amer. Desm. 1896, p. 269 ; Alg. N. Ireland, 1902, p. 47 ; Scott. 



Freshw. Plankton, I, 1903, p. 551 ; Further Contrib. Plankton Scott. 



Lochs, 1905, p. 487 ; Comp. Study Plankt. Irish Lakes, 1906, p. 87 ; 



Cushman in Bull. Torr. Bot. Club, 1907, p. 615 ; West & G. S. West, 



Phytopl. Engl. Lake Distr. 1909, p. 289 ; Brit. Freshw. Phytoplankton, 



1909, p. 174. 

 St. munitum Wood, Freshw. Alg. N. Amer. 1873, p. 154, t. 13, f. 13. 



Cells large, about \\ times longer than broad, exclud- 

 ing the processes, constriction fairly deep ; sinus nearly 

 rectangular with subacute apex ; semicells broadly 

 elliptical or subspherical. provided with 2 whorls of 

 processes ; lower whorl consisting of 9 processes, nearly 

 horizontal, 5 of which are visible in the front view; 

 upper whorl of 6 processes, ascending obliquely; pro- 

 cesses nearly as long as the body of the semicell is 

 broad, tipped with 3 spines, and with 2-7 series of 



denticulations ; body of cell smooth. Vertical view 



j 



nearly circular, with a marginal series of 9 processes, 

 and an apical series of 6 shorter processes. Chloroplast 

 axile with a central pyrenoid, and a lobe stretching into 

 the base of each process. 



Zygospore unknown. 



Length, without processes, 66-96 fx ; with processes, 

 100-1 55 \i ; breadth, without processes, 46-68 (JL ; with 

 processes, 92-160 \L ; breadth of isthmus 24-33 \L. 



ENGLAND.- -Plankton of Crummock Water and Enner- 

 dale Water, Cumberland ! Plankton of Brother's Water, 

 Grasmere and Easedale Tarn, Westmoreland ! 



WALES. Capel Curig ! (Cooke & Wills] and Llyn 

 Ogwen !, Carnarvonshire. In the plankton. 



SCOTLAND.- -Birsemore Loch and Dalbagie, Aberdeen ; 

 Tobermory in Mull, Argyle (Roy & Biss.). Plankton of 



VOL. v. 13 



