\\NTHIDIU.M. 



Forma protuberans nub. (PL CVII, fig. ).) 



A large form with the semicells elliptic-hexagonal, 

 and with a small protuberance in the middle of the 

 scrobiculated central area. 



Length 58 p. ; breadth without spines 52 p,, with 

 spines 79 p, ; breadth of isthmus 15 JJL; thickness :}(') p.. 



SCOTLAND.- -In the plankton of Loch Laxadale, 

 Harris, Outer Hebrides ! 







Var. quadricornutum (Hoy & Biss.) W. & G. S. West. 



(PI. CVII, fig. 4.) 



Xaiithidium quadricornutum Roy & Biss. Scott. Desm. 1893, p. 245, t. 4, 



f. 5. 

 A", tetracentrotum Wolle var. quadricornutum (Roy & Biss.) W. & G. S. 



West, Notes Alg. II, 1900, p. 21)1. 



Spines shorter, with the pairs rather irregularly 

 disposed; central area large, not much thickened and 

 not protuberant, densely scrobiculate. 



Length 47'5-50/x; breadth (without spines) 45- 

 47*5 p.-, breadth of isthmus 14-1 5 p.. 



SCOTLAND.- -In a pool near Durris Bridge, Kincardine 

 y (J- Bissett). 



As we pointed out in the 'Journal of Botany/ in 1900, 

 this variety differs very little from the American plant first 

 described by Wolle. 



> 



4. Xanthidium controversum }Y. & G. S. West. 



(PI. CVII, figs. 5, G.) 



Xanthidium antilopceitm (Breb.) Kiitz. 'forma' W. & G. S. West, Some 



N. Amer. Desm. 1896, p. 252, t. 16, f. 1. 

 X. controversum W. A: (.T. S. West, Some Desm. U. S. 1S98, p. 298, t. 17, 



f . 2 ; Cushnian in. Khodora, vii, 1905, p. 260; Nordst. Index Desmid. 



Suppl. 1908, p. 41. 



Cells rather under medium size, 14- times lono-er than 



o o 



broad (without spines), deeply constricted, sinus 

 open and acute-angled, with an acuminate apex ; 

 semicells elliptic-hexagonal, upper lateral margins some- 

 times slightly retuse, apex widely truncate, lateral and 

 apical angles furnished with a single spine (or some- 



