38 BRITISH DESMIDIACE^;. 



and they often occur in pairs owing to the copious mucus 

 holding the two individuals in the position they occupied 

 immediately after division. 



The genus is divided into two sections according to the 

 axile or parietal disposition of the chloroplast. 



Section 1. Monotseniae Rabenh. ; em. Liitkem. 



Cliloroplasts parietal, band-like ; pyrenoids few and 

 scattered. 



1. Spirotsenia condensata Breb. 

 (PL II, figs. 7-10.) 



Spirotsenia condensata Breb. in Balls' Brit. Desm. 1848, p. 179, t. 34, f . 1 ; 

 De Bary, Conj. 1858, p. 75, t. 5, f. 12 ; Arch. Coirj. Spirotaen. 1867, 

 p. 186, t. 8, f. 5-11 ; Rabenh. Flor. Eiu-op. Algar. Ill, 1868, p. 146 ; 

 Wolle, Desm. U.S. 1884, p. 33, t. 3, f. 21, 22; Cooke, Brit. Desm. 

 1886, p. 50, t. 19, f . 3 ; West, Alg. W. Ireland, 1892, p. 133 ; Liitkem. 

 Gatt. Spirotseii. 1895, p. 53 ; Nordst. Index Desmid. 1896, p. 78 ; West 

 & G. S.West, Alg. S. England, 1897, p. 478 ; West & G. S. West, Alga-fl. 

 Yorks. 1900, p. 39. 



Cells large, cylindrical, 5-10 times longer than their 

 diameter, poles rounded ; chloroplast broad, parietal, 

 with 7-12 rather close revolutions. 



Zygospore globose ; inner wall pale brown ; outer 

 wall colourless, thick, and furnished with large areolar 

 markings. 



Length 150-270^; breadth 18-27 /u ; diam. zygosp. 

 60 A/. 



ENGLAND. Cumberland! Westmoreland! (Ralfs). 

 W. and N. Yorks! Lancashire! Leicester (Roy). 

 Warwick (Wills). Norfolk (Cooke). Gloucester (Rolfs). 

 Surrey ! Sussex (Ralfs). Kent (Ralfs). Hants ! 

 (Bennett). Devon! Cornwall ! (Ralfs). 



WALES. Greneral in the mountainous districts ! 



SCOTLAND. Greneral ! ; occasionally with zygospores 

 (Roy fy Bissett). Greneral in the Outer Hebrides ! 



IRELAND. G-alway ! Kerry ! Donegal ! Dublin 

 and Wicklow (Archer). Down ! 



Geogr. Distribution. France. Germany. Austria 

 Italy. Norway. Sweden. Denmark. Russia. Poland 



