COSMAEIUM. 31 



A small variety with depressed semicells ; apices 

 distinctly flattened but at the same time slight Iv 

 convex ; vertical view elliptic ; cell- wall smooth. 



Length 17-22 //; breadth 13-18 /u; breadth of isthmus 

 9*5-15 /u; thickness 9-16 /n. 



EXGLAXD. Epping Forest, Essex ! Xear Senens, 

 Cornwall ! 



Geoqr. Distribution. Bohemia. Italy. Spitsbergen. 

 E. Africa. 



Hansgirg includes both Norstedt's forms (1875) and 

 Delponte's " C. moniliforme var. a" in his var. minus, and in 

 this we have followed him. It would be impossible to separate 

 these various forms as they agree so closely in the shape of 

 the sinus,, although Delponte's Italian plants, of which we 

 give a figure (PL LXVIII, fig. 5), are not so depressed at the 

 apex as the others. 



It is a small variety with depressed apices similar to those 

 of C. pseudarctoum, but with a different kind of constriction 

 and an elliptic vertical view. 



65. Cosmarium subarctoum (Lagerh.) Eacib. 

 (PI. LXVIII, figs. 6-8.) 



Cosmarium globosum Bulnh. siibsp. subarctoum Lagerli. in Wittr. & Xordst. 



Alg. Exsic. 1883, no. 567; fasc. 21, 1889, p. 45; Nordst. Desm. Gronl. 



1885, p. 9, t. 7, f . 5 ; 

 C. subarctoum (Lagerh.) Eacib. Desmidyja Ciastonia, 1892, p. 385, t. 6, 



f. 24 ; West & G. S. West, Alg. S. England, 1897, p. 491 ; Comp. Study 



Plankton Irish Lakes, 1906, p. 100. 



Cells very small, about 1 J times as long as broad, 

 moderately constricted, sinus open and subrectangular 

 with a subacute apex ; semicells transversely snb- 

 elliptic, apex convex but somewhat flattened, sides 

 rounded. Side view of semicell broadly elliptic or 

 subglobose. Vertical view elliptic, ratio of axes about 

 1 : 1*3 to 1*4. Cell-wall smooth, sometimes becoming 

 yellow. Chloroplasts axile, one in each semicell, with 

 one central pyrenoid. 



Zygospore unknown. 



Length 15-21-5^; breadth 12-17 /x; breadth of 

 isthmus S'5-11'5 /x ; thickness 8*5-11 p.. 



