211 



semicells and rounded-truncate apices, which are quite 

 destitute of tubercles. 



PI. Trahrriilii is ;t more robust species tlian PI. Hli,n"iil,rr</ii, 

 witli ;i dilVrrence in the basal undulation of (lie seuiicdls, ;ind 

 with smooth ;ipices. Some of its loi-ius ;ippro;i<-li verv closely 

 PI. iini.i'iiiiiini (Keinsch) Lund. 



Forma granulata G. S. West. 



Plcurotxnium Tr<i1>i>ri<1<i forma iii-mmlnta G. S. Wcsl, Al."-a-fi Canibr 

 1899, p. m, t. ::'.)(;, f. 6. 



Cell-wall distinctly and irregularly granulate. 

 Length 486 //,; breadth at base of semicells 35 /u; 

 breadth of apices 25 /x. 



ENGLAND. Chippenham Fen, Cambridge ! 



This form is precisely an;iloo'(>us to P. Ehrenbergii v:i.r. 

 granulatum Half's. 



Forma clavata (Kiitz.) West & G. S. West, (PL XXXI, 



figs. 8, 0.) 



Doculiinii ./iii-iitum Kiitz. in Ralfs' IJrit. Desm. 1848, p. 1.16, t. 26, f. 3; 



Arch, in 1'ritch. Infus. isiil, p. 745, t. 2, f . 9 ; Cooko, Brit. Desm. 1886, 



p. 14. t. (i, f. 2 ; Eoy & Biss. Scott. Desm. 1894, p. 241. 

 Pleurotxnium clnvatum (Kntz.) De Bary, Conj. LS5S, p. 75 ; Ilalx-nh. Flor. 



Europ. Aljr. Ill, 1868, p. 141 ; De Toni, Syll. Alt;-. 1SH9, p. 897 ; W.'sl. 



Alo-. W. Ireland, 1892, p. 119. 



DiK-iilhtin Triilii'citJu. f. 1!. i-lnnitinn Ecinsch, Algenfl. Frank. 18(57, p. 1S3. 

 Plcuriit.-i'iiinni Trabecula forma clavata West & G. S. West, Alg-a-fl. Yorks 



1900, p. 58. 



Cells about 12 times longer than their diameter ; 

 semicells slightly tumid and subclavate. 



Length 300-390 /u,; breadth at base of semicells 

 22-31 /x; maximum breadth 24-32'5 /x. 



ENGLAND. Westmoreland! (liisw.tt). W., N., and 

 E. Yorks! Warwick (Will*). Sussex (lin Ifi). Hauls 

 (//"//). Cornwall (Marquand). 



WALES. Bethesda !, Capel Curig ! (rW- ^ MV//x), 

 and near Dolbadarn (Jastle ! , Carnarvonshire. Llyn 

 Coron, Anglesey ! 



SCOTLAND. Sutherland, Ross, Inverness, Nairn, 

 Aberdeen, Kincardine, Forfar, Perth ! (Uotj $ IH.wll). 

 Kirkcudbright ! 



