20<> niUTlSH DESMIDIACE2E. 



Var. fluctuatum West. (PL XXVIII, figs. 1, 



PU' a :'"! .I'll nint, coronalum var. fluctuatum West, Aly. W. Ireland, 1892. 

 p. 118, t. 1!), f. 11. 



Cells larger than in tho typical form, 11,* 14 times 

 longer than their diameter ; lateral mai'irins of the 



O O 



semicells undulate along' their entire length; basal in- 

 flation large, as in the type ; apical tubercles large, 

 11-15 in number (0-8 visible). 



Leno'tli 070-832 u; breadth at base of semicells 55- 



O 



72 /A, in middle of semicells 4353 /x, at apex 50-53 JJL. 



SCOTLAND. Khiconich, Sutherland ! Plankton of 

 Loch Fadaghoda, Lewis, Outer Hebrides ! 



IRELAND. Lough Aunierin, Galway ! 



This is the largest British Pleurotsenium and is a very 

 handsome Oesmid. Pleurotdenium cartniut mn is far from 

 coinuion and the vox. fluctuatum is very rare. In all forms of 

 this species the cell-wall is very thick and is finely scrobi- 

 culate. 



Var. robustum West. (PL XXVIII, fig. 3.) 



Pleurotsenium coronutniit var. rulustmn West, Al^. W. Ireland, 1S!)1', p. US, 

 t. 19, f. 12 ; West & U. S. West, Alg. N. Ireland, 1902, p. 26. 



Cells shorter than in the typical form, about 8 times 

 longer than their diameter; semicells with the lateral 

 margins subundulate, distinctly and somewhat suddenly 

 attenuated at the apex ; apical tubercles large, 10 in 

 number (5 visible). 



Length 460 ^ ; breadth at base of semicells 57 /a, in 

 middle of semicells 55 /x, at apex 48 ^. 



IRKLAND. Dungloe and Sproule's Lough, Donegal ! 

 Lough Derryclare, Galway ! 



Viii-. nodulosum (Breb.) West. (PL XXVII], figs. 



5-8.) 



Din'i<liniii innhilosum Bn'l). in lialf's' Brit. Desni. LS-1S, p. 155, t. 20, f. 1 ; 



Arch, in Pritch. Infua. LSG1, p. 715; Couke, Urit. Desm. 1880, p. 15, t. 0, 



f. 3. 

 l'li-in-<il;i'iiiinn >nnl id.Hxmn (llivli.) Do IJ;iry, <'")'.]. Is5s, p. 75; Delp. Desm. 



sul.alp. 1877, p. 120, t. 19, f. 1-0; Kirchn. Alg. Schlos. 1878, p. 144; 



Ilansg. 1'n.dr. Al-vnii. Uoliiu. 1NN8, p. J.S'.t, f. 112; De Toni, Syll. Al- 



1889, p. 900. 



