ARTHUODESMUS. 105 



Var. hebridarum car. nov. (PI. CXV1I, fig. 22.) 



A small variety, with the angles of the semicells 

 somewhat produced and narrower ; sides of semicells 

 faintly retuse, and apex very slightly convex in the 

 middle portion only. 



Length 15jii; breadth without spines 18'5/u,, with 

 spines 21*5 //,; breadth of isthmus 6 /x. 



SCOTLAND.- -Benbecula, Outer Hebrides ! 



7. Arthrodesmus Bulnheimii Racib. 

 (PI. CXVI, figs. 1, 2.) 



Artlirodesmiift Incus Bulnh. in Hedwigia, 1861, p. 51, t. 9, f. 3. 

 A. Bulnheimii Eacib. Desm. Nowe, 1889, p. 95, t. 16, f. 17 ; Eichler, Mat. 

 flor. Miedz. 189-i, p. 129, t. 3, f . 3-4 ; Nordst. Index Desmid. 1896, p. 70. 



Cells of medium size, or sometimes less, a little longer 

 than broad (without the spines), deeply constricted, 

 sinus narrowly linear with a slightly dilated apex ; 

 semicells transversely subrectangular, sometimes very 

 slightly widened from base to apex, sides and apex 

 slightly convex, angles slightly rounded, each apical 

 angle furnished with a long, stout, divergent spine. 

 Cell- wall smooth, punctate, or more rarely with a few 

 irregularly scattered scrobiculations. Vertical view 

 elliptic with a stout spine at each pole. 



Zygospore unknown. 



Length without spines 32-42 ^ ; breadth without 

 spines 30-40 /x; length of spines 18-27/x; breadth of 

 isthmus 7'5-9'6/x; thickness 16-20 /x. 



SCOTLAND.- -Rhiconich, Sutherland ! Harris, Outer 

 Hebrides ! 



Geoc/r. Distribution.- -Germany. Poland. Lapp- 

 mark in Norway (form). 



A. Bulnheimii is a very rare Desmid characterized by the 

 rectangular semicells and the closed linear sinus. 



Yar. subincus var. nov. (PI. CXVI, fig. 3.) 



A. Incus "forma apicibus constanter convexis" West, Alg. W. Ireland, 



1892, p. 168. 

 A. Incus var. validus forma minor W. & G. S. West, Alg. N. Ireland, 1902, 



p. 58, t. 2, f. 15. 



