80 BRITISH DESMIDIACE.E. 



Cells small, 1 J- times longer than broad, deeply con- 

 stricted, sinus narrow, sometimes linear ; semicells 

 pyramidate- truncate, ventral margin straight, apex 

 truncate, sides slightly convex, upper angles very obtuse, 

 basal angles broadly rounded, peripheral margin denti- 

 culate, showing about 26 or 28 granules, those near the 

 basal angles sometimes developing into short spines ; 

 faces of semicell granulate near the margin, granules 

 arranged in 2 or 3 concentric series round the basal 

 angles, and in about 3 series parallel to the apical 

 margin, the latter being emarginate ; granules in the 

 middle of the faces becoming smaller and scattered, 

 centre of face almost smooth. Vertical view triangular, 

 angles obtusely rounded, sides very slightly concave, 

 margins denticulate, those granules in the middle of 

 lateral margins being emarginate; angles with two or 

 three concentric series of denticulations, and with 

 two pairs of emarginate verrucee within each lateral 

 margin. 



Zygospore unknown. 



Length 30-38'5u; breadth 31-38'5(Ji; breadth of 

 isthmus 9'5-12[jL. 



ENGLAND. Mossdale Moor, Widdale Fell, N. Yorks ! 



WALES.- -Y Foel Fras, Carnarvonshire ! 



IRELAND. --Near Gweedore, Co. Donegal ! 



Geogr. Distribution . Siberia . 



Var. inornatum Rov. 



> 



St. Amellii var. inornatum Roy, Desm. Alford District, 1890, p. 208 ; Roy & 

 Biss. Scott, Desm. 1893, p. 'l7. 



Differs from the type in the granules being scattered. 

 SCOTLAND.- -Very rare, near Alford, Aberdeen (Roy 

 Biss.). 



Var. spiniferum W. & G. S. West, (PL CXXXIX, 



fig. 15.) 



St. Arnellii var. spiniferum West & G. 8. West, Al<?. N. Ireland, 1902, p. 51 r 

 t. 2, f. 38. 



