SPHCEROZOSMA. 207 



Zygbspore globose, rectangular or oblong, smooth, or 

 furnished with simple spines. 



Sphcerozosma is distinguished from all other colonial Desmids 

 by its short apical processes. The only other genus in which 

 similar processes occur is Onychonema, but here they are very 

 much longer, so long as to overlap the cells in a very characteristic 

 fashion. 



Dr. Liitkemuller in ' Zellmem. Desm.' 1902, p. 367, has expressed 

 the opinion that the short apical processes are not in themselves 

 the effective means by which the cells of the filaments are 

 united. He found that the real connecting link is a thin gela- 

 tinous cushion stretching between adjacent cells, in which the 

 processes of both are embedded. He further suggested that 

 possibly the real function of the apical processes is to counteract 

 to some extent the tendency of the filament to twist, a tendency 

 which, if allowed to become too strong, would eventually lead 

 to the breaking up of the filament. 



The processes are sometimes very delicate, and only seen with 

 difficulty. They are usually observed most readily on the free 

 ends of the filament, or on isolated cells. 



There are 5 British species of the genus, none of which is 

 abundant. 



1. Sphaerozosma Auhertianum West. 

 (PL CLIX, fig. 13.) 



Sphcerozosma Aubertianum West, Freshw. Alg. Maine, 1889, p. 206, t. 291, 

 f. 17 ; Alg. W. Ireland, 1892, p. 115, t. 19, f. 1 ; West & G. S. West, 

 Some N. Araer. Desm. 1896, p. 230, t. 12. 



Cells small, about as long as broad, or a little broader, 

 deeply constricted, sinus acute, almost linear at first, 

 then opening more widely ; semicells narrowly elliptic 

 or almost elliptic-oblong, sides and apex gently rounded, 

 lateral margins with two distant minute granules, 

 arranged vertically ; semicells in side view subspherical, 

 with the connecting processes on each side of the apex ; 

 vertical view oblong-elliptic. 



Zygospore globose or subglobose, with many long, 

 curved, and sharp spines, broad and hollow at the base. 

 Length of spines variable. 



