70 BRITISH DESMIDIACEJE. 



densely scrobiculate tumour just below the middle of 

 the apex. Side view of semicell obversely subsemi- 

 circular, with convex apex and rounded angles. 

 Vertical view narrowly oblong, with a finely scrobi- 

 culate tumour at the middle on each side, ratio of axes 

 about 1:1*3 (with the inflations). Cell-wall (apart 

 from the central tumours) finely punctate. Chloro- 

 plasts axile with a central pyrenoicl. 



Zygospore unknown. 



Length 24 ^ ; breadth 22-23 p. ; breadth of isthmus 

 6-7 JJL ; thickness 16-18 p. 



SCOTLAND.- -Bottomend, near Aboyne, Aberdeen 

 (Boy $ BisseU). 



G-eocjr. Distribufion. France. Germany (var.), 

 Galicia in Austria (var.). Sweden. Bornholm. 

 Poland. United States (var.). 



The central protuberance, which Lunclell describes as 

 "granulate/' is really finely scrobiculate., and these small 

 depressions are situated so close together as to give the 

 margin of the protuberance quite a rough appearance when 

 seen in vertical view. C. protuberans appears to be a very 

 rare species. 



The Desmicl mentioned and figured by Wille ('Xorges 

 Ferskv. Alg.' 1880, p. 33, t. 1, f. 18) as a form of C. pseudo- 

 protuberans Kirchn. is only a large form of C. protuberans 

 Lund. 



Forma paludosa/. nov. (PI. LXXI, fig. 10.) 



C. protiiberans Lund, forma G. S. West, Alga-fl. Carubr. 1899, p. 116, t. 

 394, f. 12. 



Cells more deeply constricted, apex of sinus more 

 conspicuously ampliated, and the protuberances in the 

 vertical view considerably reduced. 



Length 22-23 ju,; breadth 19-21 p,-, breadth of isth- 

 mus 5'2/x; thickness 12 ja. 



ENGLAND.- -In ditches, Chippenham Fen, Cambridge- 

 shire ! 



The cell-wall of this form is minutely scrobiculato-punctate 

 as in the type. 



