440 Annals of the South African Museum. 



oospore measures from 64 to 73 /M iu diameter, with smooth, thick 

 outer wall (Plate X, fig. E). A comparison was made with F. aureus 

 forma madagascariensis (Professor Fritsch's material), but we find 

 it agrees more closely with the type than with this form. 



2. From Weltevreden West (only asexual colonies were collected). 



3. From N'gamo and Old N'gamo (S. Khodesia), and from vleis along 



the Linyanti River (Bechuanaland Protectorate), particularly at 

 Kazungula and Kabulabula (Plate XI, figs. B, C). 



V. aureus is evidently widespread in this region of Africa. The 

 collections were made in July, i.e. midwinter, when the vleis left by 

 the rains of the previous wet season (ending March or April) were still 

 extensive. It was usually associated with V. Rousseletii and Pleodorina 

 californica (Plate XI, fig. B), and a rich phytoplankton of desmids, and 

 other unicellular, colonial, and filamentous algae. 



Except for its greater size it is similar to the V. aureus found at 

 Potchefstroom, and is characterised by the small degree of differentia- 

 tion reached by the third generation at the birth of the daughter 

 colonies, and the marked rarity of mixed colonies, the great majority 

 producing either only gonidia, only antheridia, or only oogonia. 



The number of cells is usually between 1000 and 3000, the protoplasts 

 are from 6 to 9 /i in diameter. The greatest size noted for asexual 

 colonies was 782 x 816 n ; female colonies up to 604 x 625 yu,, and males 

 up to 539 x 560 fj,, were measured (these measurements were all made 

 free on the slide, not under the pressure of a cover slip). The smallest 

 free colony measured was 182 x 194 [i, but daughters in situ with a 

 diameter of 243 p, were seen ; the largest number of daughters per 

 coenobium observed was 11. 



Platelets, always of 32 spermatozoids, measured 20 fi ; oospores 

 (up to 11 per colony) from 65 to 84 ^JL in diameter. 



B. Volvox africanus G. S. West. Plate XII, figs. A, B. 



Late in our investigations we found this species in material from 

 a pool near the wagon road leading from Kazungula to Kasani, on 

 the Linyanti River. The pool was long and shallow, about 1 foot 

 deep, and fairly clear. The Volvox association was rich large colonies 

 of V. capensis predominated, with F. aureus, V. africanus, and 

 Pleodorina californica mixed with them. The colonies of F. africanus 

 were comparatively few, and all asexual ; in most, the daughter 

 colonies numbered 4 the 2 larger opposite one another in the 



