212 I'.KITISII DKS.MIDIAi'K.i;. 



L{f:i,.\.\D. Gal way ! Dublin and Wicklow (Ar<-ln'r\ 

 Antrim ! 



(ii'otji-. Dixtrilwtion. France. Germany. Italy. 

 Sweden. United States. 



Var. rectum (Dclp.) nob. (PI. XXX, figs. 9, 10.) 



rectum Dolp. Dcsm. Sulialp. Is77, p. 129, t. 2O, f. 8-11 : 

 DC Toni, Syll. Ala;. 1SS<, p. S'.lii; West. Ali;-. W. Irclan-1, 1S'.I_>. p. ] 20 : 

 Lutkcm. Dcsm. Attersees, IS':i. p. .-,|.<; : ];..y ^ Hiss. Sd.tt. Dcsm. isi'l. 

 p. 21.2 : Nordst. Index Desin. 1896, p. 222. 



Peniinii i-i'i-txm (Dclp.) Willo, Sydamerik. Algfl. 1884, p. 22. 



Docidium rectum (Dolp.) Wolle, in Bull. Torr. Bot. C'lul), 1S85, p. 2. 



Pleurotxnium maximum West, Alg. W. Ireland, 1892, p. 119. 



PI. maximum var. occidentalc West, Alg. Eng. Lake Distr. 1892, p. 719. 



Cells rather smaller than in the type, straight, 

 12-18 times longer than their diameter ; lateral margins 

 of semicells above the slight basal inflation straight ; 

 cell- wall often smooth. 



Length 212-408 )a ; breadth at base of semicells 

 22-23 jji ; breadth of apices 14-20 /JL. 



ENGLAND. Enbridge Lake, Hants. (7?o//). 



WALES. Capel Cnrig, Carnarvonshire (Roy). 



SCOTLAND. General (Roy $* THwft). We have 

 only found it in Aberdeen, Ross, Inverness, Suther- 

 land, and the Outer Hebrides ! 



IRELAND. Cromagioun, Kerry ! 



Geofjr. Distribution. Italy. Austria. Hungary. 

 Galicia. Norway. Sweden. Central China. India. 

 New Zealand (var.). Australia, United States. Brazil. 



It is impossible to retain Pleurotasnium rectum, Del]). :is a 

 species separate from PI. Trobecula (Ehrenb.) Niii>'. It only 

 dilf'ers in the somewhat smaller size of the cells and the 

 straighter lateral margins of the semicells. It is IVecjiient in 

 some districts of Scotland and Ireland, but is very uncommon 

 in I'hiu'lancl. 



Var. rectissimum var. nor. (PL XXX, figs. 14, 15.) 



Cells more elongate than in the type, 26-30 times 

 longer than their diameter, rigidly straight; semicells 

 with the slight basal undulation of the type, very 



