138 BRITISH DESMIDIACE2E. 



5. Cosmarium Lundellii Delp. 

 (PI. LVII, figs. 1, 2). 



Cosmarium Lundellii Delp. Desm. subalp. 1877, p. 13, t. 7, f . 62-64 ; Wille, 

 Norges Ferskv. Alg. 1880, 1, p. 33 ; Sydamerik. Algfl. 1884, p. 47, t. 3, 

 f. 89 ("forma ") ; De Toni, Syll. Alg. 1889, p. 956 ; Nordst, Index Desm. 

 1896, p. 160 ; West & G. S. West, Fresliw. Alg. Ceylon, 1902, p. 12. 



Ursinella Lundellii Kuntze, E,evis. gen. plant. 1891, p. 925. 



Cosmarium subcirculare Turn. Freshw. Alg. E. India, 1893, p. 52, t. 8, f. 3; 

 t. 9, f. 27, 37. 



Cells large, subcircular, about as long as broad (or a 

 little longer), deeply constricted, sinus linear with a 

 dilated apex ; semicells subsemicircular or pyramidate- 

 semicircular, basal angles broadly rounded. Side view 



O f 



of semicell subcircular. Vertical view elliptic, ratio of 

 axes 1 : 1'94, poles slightly drawn out. Cell-wall 

 punctate, generally thickened in the centre of the 

 semicells. Chloroplasts axile, with prominent ridges, 

 and with two laro-e pvrenoids. 



O It/ 



Zygospore unknown. 



Length 79-88 /* ; breadth 69-79 ^ ; breadth of isth- 

 mus 30-41 //, ; thickness 42-45 ILL 



ENGLAND. Mousehole Cave, Cornwall ! 



Geocjr. Distribution. Germany. Gralicia in Austria. 

 Italy. Norway. Poland. Central China (forma). 

 India. Central and E. Africa. Madagascar. Brazil. 

 Ecuador. Argentina. 



This species is much more abundant in the tropics than in 

 temperate climates, and quite a number of distinct varieties 

 of it exist. It differs from C. Ralfsii Breb. in its somewhat 

 smaller size, its less deep constriction and consequently 

 broader isthmus,, in the more rounded basal angles of the 

 semicells, and in its axile chloroplasts. 



The breadth of the isthmus as compared with the breadth 

 of the semicell is as 1 : 4'3 in C. Ralfsii, whereas in C. Lundellii 

 it is only 1 : 2*5. 



Var. ellipticum West. (PI. LVII, figs. 3, 4.) 



C. Lundellii var. ellipticum West, New Brit. Fresliw. Alg. 1894, p. 5, t. 1, 

 f. 11. 



Cells smaller than in the type, about 1-J- times longer 

 than broad, with a narrower isthmus. 



