182 BRITISH DESMIDIACE^. 



into short processes with 3 tiny spines at their apex. 

 Vertical view triangular, sides concave, and with two 

 short diverging processes with bifid apices at the base 

 of each angular process. 



Zygospore unknown. 



Length, 22*5 [i ; breadth, including processes, 39 [i ; 

 breadth of isthmus 13 '5 y*. 



SCOTLAND. New Galloway, Kirkcudbright ! 



Geogr. Distribution.- -W '. Greenland (var.). 



This species seems to be very closely allied to St. arcuatum 

 Nordst. Its lateral angles are, however, not so divergent as in 

 that species, nor are the apical processes so long or erect. In 

 the vertical view the angles are also distinctly inflated in St. 

 arcuatum, whereas in St. amphidoxon the body of the cell gradually 

 tapers at the angles into the processes. 



168. Staurastrum megalonotum Nordst. 

 (PL CLIV, fig. 13.) 



Staurastrum megalonotum Nordst. Desm. Arctoae, 1875, p. 35, t. 8, f. 38 ; 

 Boldt, Desm. Gron. 1888, p. 39 ; De Toni, Syll. Alg. 1889, p. 1222 ; Cush- 

 man in Rhodora, 1905, p. 263. 



Cells of medium size, nearly as long as broad, deeply 

 constricted, sinus open arid acute ; semicells in front 

 view subhexagonal fusiform, apex somewhat produced, 

 truncate or slightly concave, upper angles ending in a 

 spine, lateral angles produced slightly and also ending 

 in a spine, upper margin of lateral angles gently con- 

 cave, lower margins nearly straight ; angles provided 

 with several series of denticulations. Vertical view 

 quadrangular, sides concave, angles slightly pro- 

 duced, ending in a spine, and with concentric acute 

 denticulations, lateral margins with acute granules near 

 the angles, but smooth in the median part, with two 

 spines or spinulose processes just within each lateral 

 margin ; centre of apex smooth. 



Zygospore unknown. 



Length, without spines, 42-46 (j. ; breadth, including 

 spines, 62 \L ; breadth of isthmus 16-21 [i. 



