212 BKITISH DESMIDIACE.E. 



obtuse ; semicells broadly oval, isthmus slightly 

 elongated ; lateral view of cell oblong-elliptic, sides 

 slightly concave ; vertical view oblong with rounded 

 ends and 4 minute attaching processes on the long 

 margins. Cell-wall usually smooth, sometimes with 

 horizontal rows of minute granules. Chloroplasts axile, 

 one in each semicell with a central pyrenoid. 



Zygospore rather large in proportion to the size of 

 the cells, oval or spherical, wall quite smooth. Ralfs 

 (' Brit. Desm.' 1848) records the occurrence of lateral 

 conjugation in this species. 



Length 7 "5-12^ ; breadth 7-14 fi ; breadth of isth- 

 mus 3* 5-6 "5 [i ; thickness 5-7 u ; length of zygospore 

 10-2-16 [i ; breadth 9-11 ^. 



ENGLAND. - - Cumberland ! Westmoreland ! (Rolfs). 

 Lancashire (Rolfs}. W., N., and E. Yorks ! Leicester 

 (Roy}. Burnham Beeches, Bucks ! Warwicks (Wills). 

 Gloucester (Rolfs}. Surrey ; zygospores from Putten- 

 ham arid Thursley Commons ! Sussex ; Kent (Rolfs}. 

 Hants ! (Roy} ; zygospores from New Forest ! Devon \ 

 (H orris}. Cornwall ! (Rolfs}. 



WALES. Snowdon !, Llyn Padarn !, Llyn Idwal !, 

 Capel Curig ! (Cooke & Witts) and Glyder Each (at 

 2200 feet) !, Carnarvonshire. Radnor ! 



SCOTLAND. General and frequently conjugated ! (Roy 

 & Biss.}. Shetlands ! 



IRELAND.- -General ! Wicklow ! Plankton of Galwav ! 



t> 



Geogr. Distribution- -Erance. Germany. Switzerland. 

 Galicia in Austria. Hungary. Servia. Italy. Portugal. 

 Norway. Sweden. Denmark. Finland. S. Russia. Nova 

 Zembla. Spitzbergen. Greenland. India. Australia. 

 Abyssinia. Central Africa. United States. N.W.Canada. 

 Brazil. 



Var. subquadratum var. nov. (PI. CLX, figs. 4, 5.) 



Spli. excavatum var. subquadratum West & G. S. West in manuscript. 



Cells relatively broader than in the type, deeply con- 

 stricted, sinus narrow and obtuse at its apex ; semicells 



