STAURASTRUM. 39 



Staiirastnim denticulatuin Arch, in Pritch. Inf. 1861, p. 738 ; Rabenh. Flor. 



Europ. Alg. 1868, p. 213; Kirchn. Alg. Schles. 1878, p. 169; Hansg.. 



Prodr. Algenfl. Bohm. 1888, p. 214 ; De Toni, Syll. Alg. 1889, p. 1163 ; 



West, Alg. N. Wales, 1890, p. 16, f. 27 ; West & G. S. West, Alg. S. 



England, 1897, p. 493 ; Comp. Study Plankton Irish Lakes, 1906, p. 103 : 



Gutwin. Flor. Alg. Mont, Tatr. 1909, p. 470. 

 DidyittitHum (Staurastrum) Tigurinum Reinsch, Algenfl. Frank. 1867, p. 161. 



Cells small, about as long as broad, or a little shorter, 

 deeply constricted, sinus acute-angled, and opening 

 widely ; semicells subelliptical or fusiform, dorsal margin 

 slightly convex in the middle, ventral margin strongly 

 so ; angles of semicell obtuse and tipped by two minute 

 spines. Cell- wall rough with tiny granules confined to 

 the region of the angles, and arranged in two or three 



o o * o 



concentric rings around them. Vertical view triangular, 

 sides straight or very slightly concave, angles obtusely 

 rounded. 



Zygospore unknown ? 



Length 24-35 u. ; breadth 20-40 u. : breadth of isth- 

 mus 7-1 4 [x. 



ENGLAND.- -Plankton of Ennerdale Water and Wast 

 Water, Cumberland! Red Tarn, Hawes Water and Gras- 

 mere, Westmoreland ! Epping Forest, Essex ! Worcs ! 



WALES.- -Ffestiniog, Merioneth ! In the plankton ! 



IRELAND.- -Minister and Connaught (Adams). Plank- 

 ton of Mayo and Kerry ! 



Geogr. Distribution. Germany. Galicia in Austria. 

 Spain. Sweden. Denmark. Finland. Poland. N. Russia 

 Faeroes. Australia. Central Africa. Azores. Colombia, 

 S. America. 



This species is distinguished from St. Avicula Breb. by its 

 granulation, there being only two or three series of distinct 

 granules round the angles, and the cells are also proportionately 

 broader. 



The zygospore of this species has not hitherto been figured. 

 Amongst some unnamed drawings by the late Professor G. S. West 

 is one. however, which is reproduced on PL CXXXIII, fig. 15. 

 This drawing had not been named by Professor West, but it evi- 

 dently belongs either to St. denticulatum or St. Avicula. As far 



v O 



as the characters can be seen from the empty semicells in their 



