STAURASTRUM. 117 



This species is only known in the British Isles from one 

 locality in western Ireland, and is apparently one of those 

 species which can only flourish in waters draining from the older 

 and harder palaeozoic rocks. It is very similar in appearance to 

 St. PseudosebaUi Wille var. bicorne Boldt ('Sibir. Chloroph/ 

 1885, t. 6, f. 36), but differs in the more complicated lateral 

 margins of the semicells. 



It also differs from St. Pseudosebaldi var. tonsum Nordst. 

 ('Freshw. Alg. Xew Zealand/ 1888, p. 36, t. 4, f. 4) in the non- 

 fusiform shape of the end view as well as in its stronger apical 

 warts. St. bicorne Hautpfl. ? forma Borge (' Sverig. Chloroph.' II, 

 1895, p. 24, t. 1, f. 15) is a form of St. Duacense, differing only in 

 its rather larger size and in the apical teeth of the processes. 



122. Staurastrum bicorne Hauptfl. 

 (PI. CXLIII, fig. 17.) 



St. bicorne Hauptfl. Zellmembr. u. Hiillgallerte Desm. 1888, p. 37, t. 3, 

 f. 21, 24, 27 ; Borg. Bornholm. Desm.-fl. 1889, p. 148, t. 6, f. 9 ; De Toni, 

 Syll. Alg. 1889, p. 1210; Roy & Biss. Scott. Desm. 1893, p. 17; Him, 

 Desm. Finnl. 1903, p. 19 ; Cedergren, Sverig. sotvattensalg. 1913, p. 23. 



Cells of medium size, about 1| times broader than 

 long, including the processes, sinus becoming very wide 

 towards the exterior ; semicells subtriangular, rapidly 

 widening towards the apex, sides concave, apex very 

 slightly convex, angles of semicell gradually attenuated 

 to form fairly long, stout, and nearly horizontal processes,, 

 which are provided with several series of denticulations,. 

 and are bifid (?) at their apex ; upper margin of face 

 with two transverse series of about 5-8 verrucae. Ver- 

 tical view narrowly fusiform, lateral margins verrucose 

 in the middle and with another series of verrucae just 

 within each margin ; processes with denticulations. 



Zygospore unknown. 



Length 52 (i ; breadth, including processes, 72 jj. ; 

 thickness 18*5 {/. ; breadth of isthmus 13*4 pi. 



SCOTLAND.- -Birsemore Loch, Aberdeen (Roy & Biss.). 



Geogr. Distribution. Germany. Bornholm (var.). 

 Finland. Sweden. Australia (var.). 



