172 BRITISH DESMIDIACE.E. 



Cells small, about as long as broad, including the 

 processes, deeply constricted, sinus widely open ; semi- 

 cells elliptical, dorsal margin only slightly convex, 

 ventral margin more strongly so ; semicells produced at 

 the angles to form short solid processes deeply bifid at 

 the apex, the two teeth lying in the same vertical plane ; 

 with two accessory spines (also occasionally bifid), 

 projecting almost vertically from the apex between each 

 pair of angles. Vertical view triangular, sides very 

 slightly convex, angles broadly rounded and then 

 slightly produced into a short solid process, with a pair 

 of simple or bifid spines projecting from the apex across 

 each lateral margin. Cell-wall with about 2 obscure 

 series of minute granules round each angle. 



Zygospore unknown. 



Length 21-30 pi ; breadth 22-34 (j- ; breadth of isth- 

 mus 5-9 \JL . 



ENGLAND.- -Helvellyn, Westmoreland ! Cocket Moss, 

 near Giggleswick ; Penyghent ; Whernside ; Mossdale 

 Moor, Widdale Fell, W. Yorks ! Mickle Fell and Lund's 

 Fell, N. Yorks ! 



WALES. Moel Siabod, bog between Glyder Fach and 

 Llugwy, y Foel Fras, and Tal-y-fan, Carnarvonshire ! 

 Ffestiniog, Merioneth ! 



SCOTLAND.- -Hoy, Orkneys ! 



IRELAND. Near Gweedore, Donegal ! Achill Island 

 and Clare Island, Co. Mayo ! Boggy inlet of Lough 

 Neagh. 



Geogr. Distribution. Sweden. United States. 



St. aciculiferum really has very little affinity with any other 

 species of Section I, but strictly speaking it belongs here. It was 

 originally described as a variety of St. Avicula, but whereas the 

 angular spines of this species are attached separately to the 

 ' body ' of the semicell, in St. aciculiferum there is a distinct 

 though short solid process, deeply bifid at its apex. The apical 

 spines may be considered well developed denticulations of the 

 series of small granules round the angles ; they are very often 

 bifid. 



