154 BRITISH DESMIDIACEJ:. 



relative proportions. In the typical form the apices of the 

 semicells are very slightly (almost inappreciably) flattened and 

 the sinus is fairly deep. 



The chloroplasts are very characteristic. They are parietal 

 bands similar to those present in C. Ralfsii, but are broader 

 with more serrated edges. The number of bands in each 

 semicell is not constant, and each band possesses several small 

 ellipsoidal pyrenoids. 



In the f Alg. of W. Ireland' p. 163, the zygospores of 

 C. Cucumis were described as u globose and smooth," but we 

 are now uncertain as to the identity of the species in question. 

 It mav have been C. Sultcucumis or some other allied form, as 



a/ 



the measurements (length 54-57 fj.; breadth 30-31 /it) are not 

 those of typical C. Cucumis. 



Var. helveticum Nordst. 



C. Cucumis var. helveticum Nordst. in Wittr. & Nordst. Alg. Exsic. 1880, 

 No. 378 ; and in fasc, 21, 1889, p. 43 ; Eoy & Biss. Scott. Desm. 1894, 

 p. 44. 



Cells smaller, semicells more rapidly attenuated 

 towards the apex ; cell-wall densely and minutely 

 scrobiculate. 



Length 48-56 M ; breadth 26-36 p; breadth of 

 isthmus 10-12 /LI; thickness 22-26 /u. 



ENGLAND.- -Delamere, Cheshire (Roy). Leicester- 

 shire (Roy). 



WALES.- -Glyder Fawr and Pen-y-gwryd, Carnar- 

 vonshire (Rot/). 



SCOTLAND.- -Inverness, Aberdeen, Kincardine (Roy fy 

 Sis sett). 



Geogr. Distribution . Switzerland. 



We have not seen this variety. Nordstedt states that it 

 strongly resembles C. subquadratum Nordst. and C. variolatum 

 Lund. 



Var. magnum Racib. (PL LIX, figs. 21, 22.) 



C. Cucumis "forma major noil tarn, prof uncle constricta quaru anglica, 

 membraiia crassa/' Nordst. Desm. Arctose, 1875, p. 29, t. 8, f. 28; Boldt, 

 Desm. Groulancl, 1888, p. 11 ; Borg. Bornholm. Desm.-fl. 1889, p. 146 ; 

 Eoy & Biss. Scott. Desm. 1894, p. 44. 



C. Cucumis o.magna Eacib. Xonn. Desm. Polon. 1885, p. 70; West & G. S. 

 West, Fresliw. Alg. Orkneys and Shetlands, 1905, p. 15 (sep.). 



