56 BRITISH DESMIDIACEJE. 



This variety is one of tlie very handsomest of British 

 Desmids. The spines are greatly elongated and much 

 furcate, the branches reminding one of the tynes of an 

 antler. 



2. Xanthidium subhastiferum West. 

 (PI. CVI, %s. 5-9.) 



Xanthidium snbliastifernm West, Alg. W. Ireland, 1892, p. 166, t. 22, f. 4; 



W. & G. S. West, Scott. Freshw. Plankton, I. 1903, p. 540, 1. 16, f . 4-5 ; 



Further Contrib. Freshw. Plankton Scott. Lochs, 1905, p. 485 ; Couip. 



Study Plankton Irish Lakes, 1906, pp. 85, 102 ; Brit. Freshw. Phyto- 



plankton, etc. 1909, p. 180. 

 X. quadricomutum Roy & Biss. forma longispina Borg. Freshw. Alg. 



Faeroes, 1901, p. 229, t. 7, f. 13. 



Cells rather under medium size, about as long as 

 broad, deeply constricted, sinus acute-angled, open, 

 sometimes acuminate at the apex ; semicells elliptic 

 or oblong-elliptic, often slightly flattened at both base 

 and apex, each lateral margin furnished with two 

 simple divergent spines situated in the same vertical 

 plane ; in the centre of the semicell with a small, 

 rounded, thickened area. Side view of semicell 

 circular. Vertical view elliptic, with an elongated 

 spine at each pole, and with a slight thickening, 

 generally faintly protuberant, at the middle on each 

 side. 



Zygospore unknown. 



Length 43-54 ^ ; breadth without spines 44-53*5 ^ ; 

 breadth with spines 64-86 p. ; length of spines 12'5- 

 18 /A; breadth of isthmus 13-19 ju, ; thickness 25-29 p. 



SCOTLAND. Plankton of Lochs nan Cuinne and 

 Grhriama, Sutherland (.7. Murray) ! Plankton of Loch 

 Luichart, Ross ! Plankton of Loch Morar and Loch 

 Shiel, Inverness ! Plankton of Loch Fadaghoda, Lewis, 

 Outer Hebrides ! 



IRELAND.- -In the plankton of the small lakes between 

 Clifden and Roundstone, Glalway ! Lough Griiitane and 

 Glen Caragh, Kerry ! Common in the plankton of the 

 lakes of Kerry ! 



Geoyr. Distribution. Faeroes. 



