66 
Transactions of the Royal Society of South Africa. 
not uncommonly several of tliem occur together in a common sheath 
(Fig. 27, A). The vegetative cells are 5-6 [x in diameter (rather wider 
dimensions were observed in the other South African material) ; the 
heterocvsts are slightlv wider and spherical or somewhat elliptical in shape 
(Pig. 27). 
This form has been referred to the above species because of its general 
habit and other points of agreement, but in the absence of spores the 
reference is uncertain. The frequent elliptical shape of the heterocysts is a 
point of divergence, but it may be noted that G. S. West (Brit. Freshw. 
Alg., 1904, p. 328, fig. 160, B, C) figures heterocysts, which are elliptical, for 
this species. 
