208 BRITISH DESMIDIACE^E. 



Cells larger than in the type, 20-23 times longer 

 tlmn their diameter; basal inflation prominent and 

 lateral margins gently undulate from base to apex. 



Length (500-700 /A ; breadth in middle of semicells 

 28-30 /A, at apices 26-27 p. 



( iroijr. Distribution. Austria. Hungary. Sumatra. 



The true var. -nvditlntn-m Schaarschm. has not been ob- 

 served in the British Isles, but a form has been found in 

 Cambridgeshire which approaches very close to it (r'xlr (i. S. 

 West, Alga-fl. Cambr. 1899, p. 113). The upper third of the 

 semicells was destitute of undulations, otherwise it would not 

 luive differed from Schaarschmidt's variety; length 709 /i; 

 breadth at base of semicells 40/<, in middle of semicells 3.1 /, 

 at apices 27 //. This form is figured on PI. XXX, f. 4. 



5. Pleurotaenium tridentulum (Wolle) West. 

 (PI. XXX, figs. 5, (>.) 



Docidium tridentulum Wollc, in Bull. Torr. Bot. Club, 1882, p. 14 ; Dosm. 



U.S. 1884, p. 52, t. 10, f. 10 ; DC Toni, Syll. Al.o-. 1889, p. 874; Eoy & 



Biss. Scott. Desm. 1894, p. 242; Nordst, Index Desm. 1896, p. 25s. 

 D. ,SVcy</ ,-mti Eoy in Scott. Naturalist, 1883, p. 39. [This is not Clostcriu> 



Sri'jil ,-inn Kiitz.] 



Fleurotxnium truh'iitidum (Wollo) West, Alp;. W. Ireland, 1892, p. 120. 

 7Y/Mfm tridentulum Eichl. & Eacib., 1893; Eichler, Mat. flor. Miedz. 



1894, p. 57. 

 rieurotcenium Sceptrum West & G. S. West, Some N. American Desm. 



ls9(i, p. 235, t. 13, f. 6 ; Some Desm. U.S. 1898, p. 285; Alg. N. Ireland, 



19(12, p. 26. 



Cells rather small, narrow, about 20 times longer 

 than their diameter; semicells gradually attenuated 

 from base to apex, with a slight basal inflation, lateral 

 margins straight ; apices truncate, furnished with 

 four sharp spines or teeth ; cell-wall smooth. 



Zygospore subglobose and smooth. 



Length 211-320 ^ ; breadth at base of semicells 12*5- 

 1()/x; breadth at apex (V5-8'3 /i ; diam. zygosp. :U /A. 



SCOTLAND. Poolewe, Ross; Brin (Ilnij HisgeM) and 

 Moii I art, Inverness ! Head of Glen Coe, and in Mull, 

 Argyll (I !.<>i/ cj- Jiiwtt). 



1 1, 1 K LAND. Near Glenties, Donegal ! 



(ii'otjr. Distribution. Poland. India (form). W, 

 Indies. United States. 



