116 BRITISH DESMIDIACE.E. 



verrucse somewhat reduced ; with a double series of 

 granules round the base of the semicell. 



Length 46-49 (JL ; breadth, including processes, 63-70 pt ; 

 breadth of isthmus 10'5 pi. 



IRELAND. Near Lough Magrath, Donegal ! 



The double ring of granules round the base of the semicells 

 and the slight reduction of the apical emarginate warts are 

 characters which at once distinguish this variety. It bears a 

 certain resemblance to St. Pseudosebaldi Wille, but the body of 

 the plant is relatively larger, and the granulation is different. 

 In the vertical view the sides are quite smooth, all the verru- 

 cations being within the margin as in typical St. Manfeldtii. 



121. Staurastrum Duacense W. & G. S. West. 

 (PL CXLVIII, fig. 1.) 



Staurastrum Pseudosebaldi subsp. duacense West, Alg. W. Ireland, 1892, 



p. 184, t. 24, f. 1. 



St. bicorne ? Borge, Sverig. Chlor. II, 1895, p. 24, f. 15. 

 St. Duacense W. & G. S. West, Brit. Freshw. Phytoplankt. 1909, p. 202. 



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

 including the processes, constriction fairly deep, sinus 

 acute ; semicells cuneate, broadening towards the apex, 

 not inflated at the base, but sometimes with a minute 

 granule on each lateral margin near the sinus ; a.pex 

 broad and straight, with a row of emarginate verrucse ; 

 angles produced to form long, horizontal processes, bifid 

 at their extremity ; dorsal margin of processes verrucose, 

 verrucae reduced to simple denticulations towards the 

 tips ; ventral margin of processes similarly ornamented. 

 Vertical view oval, the poles produced to form long 

 processes tipped with a spine, margins smooth, with a 

 series of emarginate verrucse just within. Chloroplast 

 axile with a central pyrenoid and 5 or 6 ridges. 



Zygospore unknown. 



Length 32-38 \L ; breadth, including processes, 55-67 pi ; 

 breadth of isthmus 9-11 \L ; greatest thickness 18 JJL. 



IRELAND. Ballynahinch and Roundstflne, Galway ! 



Geogr. Distribution. Scandinavia. 



