174 BRITISH DESMID1ACEJS. 



Var. Cracoviense Racib. 



G. contractum Kirchn. e. Cracoviense Racib. Nonn. Desm. Polon. 1885, p. 84, 

 t. 10, f. 10 ; Roy & Biss. Scott. Desm. 1894, p. 44. 



Semicells obtrapezoid, sides divergent and almost 

 straight, basal and upper angles rounded, apex slightly 

 convex. 



Length 31-34 /,; breadth 22-26 /i; breadth of 

 isthmus 8-9 ju; thickness 16*5-19 /n. 



SCOTLAND. Dinnet, Aberdeen (Roy fy Bissetf). 



29. Cosmarium subcontractum West & G. S. West. 



(PL LXI, figs. 36, 37.) 



Cosmarium subcontractum'Wesb and G. S. West, Further Contrib. Freshw. 

 Plankton Scott. Lochs, 1905, p. 484 [name only] ; Freshw. Alg. Ork- 

 neys and Shetlands, 1905, p. 20, t. 1, f. 21. 



Cells small, a little longer than broad, very deeply 

 constricted, sinus narrow near the apex but widely 

 open outwards ; semicells obversely semicircular, with 

 a broad and almost straight apex, upper lateral angles 

 rounded ; side view of semicell circular. Vertical view 

 elliptic, ratio of axes about 1 : 1*7. Cell-wall minutely 

 punctate. Chloroplasts axile with one central pyrenoid. 



Zygospore unknown. 



Length 32- 5-34 /LI; breadth 30-31*5 ^; breadth of 

 isthmus 7-8*5 /^; thickness 15-15*5 p. 



SCOTLAND.- -Bressay, Shetlands ! 



This species stands nearest to C. contractum Kirchn.,, but 

 is distinguished by its broad, truncate apex. This feature 

 c'auses the cells to be proportionately shorter. 



30. Cosmarium subaversum Borge. 

 (PI. LXI, fig. 38.) 



Cosmarium subaversum Borge, Algologiska Notiser, 1897, p. 211, t. 3, f . 1. 



Cells small, about 1^ times longer than broad, 

 moderately constricted, sinus open and subrectangular ; 

 semicells obsemicircular, upper angles well rounded, 



