178 BRITISH DESMIDIACEJ:. 



Geogr. Distribution. Germany . G-alicia in Austria. 

 Norway. Sweden. Bornliolm. Finland. Faeroes. 

 Iceland. Spitzbergen. Uruguay. 



There are two very strong reasons for referring- this variety 

 to C. depressum (Nag.) Lniid. rather than to C. PJiaseolus 

 Breb. In the first place, there is an entire absence of the 

 central protuberance which is a characteristic feature of all 

 forms of C. PJiaseolus ; secondly, it is associated in large 

 numbers with numerous specimens of C. depressum in the 

 plankton of many of the lakes of the British Islands. Numer- 

 ous intermediate forms occur in the plankton which clearly 

 connect it with the more rounded typical forms of C. depressum. 

 It is very variable in size and also in the width of its isthmus. 



Var. reniforme var. nov. (PL LXII, fig. 10.) 



Cells rather small; semicells narrowly reniform, 

 sinus slightly open. 



Length 21 fj. ; breadth 26 /n ; breadth of isthmus 

 6-5,/. ' 



ENGLAND. Helvellyn, Westmoreland ! 



This variety differs from (7. subdepressum West & Gr. S. 

 West in the open sinus, the smooth cell-wall, and the 

 presence of only one pyrenoid in each semicell. 



83. Cosmarium subquadrans sp. nov. 

 (PI. LXII, figs. 11-13.) 



Cells small, a little broader than long, oblong- 

 quadrate, very deeply constricted, sinus very narrowly 

 linear, slightly dilated at the extremity; semicells 

 transversely oblong, basal angles obtuse, sides almost 

 parallel in the lower half, upper half well rounded to 

 form the upper angles, apex broad and truncate 

 (slightly convex). Side view of semicell circular. 

 Vertical view fusiform elliptic, ratio of axes about 

 1 : 2*14. Cell-wall smooth. Chloroplasts axile, each 

 with two pyrenoids. 



Zygospore unknown. 



