260 BRITISH DESMIDIACEJE. 



Roya obtusa (Breb.) W. & G. S. West, 

 (PI. CLXVII, fig. 6.) 



The zy go spores of R. obtusa var. montana W. & G. S. West 

 (vol. i, p. 108) have been discovered by Harris in Devonshire, 

 and figured by him in ' Journ. Quek. Micr. Club,' 1917, t. 19 r 

 f. 11. They are oval, about 20 /i long and 13 /t wide, and are 

 rather different in form from the zygospores of the typical form, 

 which, according to Kirchner, are spherical (cf. vol. i, p. 107). 



Roya cambrica W. & G. S. W. (vol. i, p. 108). 

 Forma limnetica W. & G. S. W. (PL CLXVI, fig. 14). 



Roya cambrica forma limnetica W. & G. S. W. in Period. Plankt. Brit. Lakes, 

 1912, p. 430, t. 19, f. 11, 12. 



A form with the apices of the cells very truncate. 

 Length 141-183 p ; breadth (in middle) 6(ji ; breadth 

 of apices 4 '4-5 [ju 



SCOTLAND.- - Plankton of Loch Katrine, Perthshire. 



Genus CYLINDROCYSTIS Breb. 

 Cylindrocystis Jenneri (Ralfs) West (vol. i, p. 77). 



Penium Jenneri Ralfs in W. & G. S. W. Brit. Desm., vol. i. p. 77. 

 Cylindrocystis Jenneri (Ralfs) West, Liitkem. Gattung Penium, 1905, 

 p. 336. 



The possibility of this species belonging to the genus Cylindro- 

 cystis was suggested in vol. i, p. 78, and that this suggestion was 

 a correct one has been confirmed bv Dr. Lutkemiiller. 



*/ 



[CYLINDROCYSTIS OBESA W. & G. S. West (vol. i, p. 60) and C. 

 ROSEOLA Turn. (vol. i, p. 62) may according to Liitkem. (' Gattung 

 Cylindrocystis' 1913) remain provisionally in the genus Cylindro- 

 cystis, but they should be regarded as doubtful species of the 

 genus until they have been examined from the point of view of 

 cell-wall structure. C. DIPLOSPORA Lund., and C. MINUTISSIMA 

 Turn., are to be transferred to the genus Cosmariiim. Vide 

 infra, p. 266.] 



