Fresh-water Alga. 79 



The genus Dactylococcus is well established by the species 

 D. bicaudatus, A. Br., and D. dispar, W. & G. S. West. 



Stages of Sccnedesmus obliquus are often observed, and can easily 

 be obtained in cultures, agreeing almost exactly with Nageli's 

 original species D. infusionum. But even if D. infusionum is to be 

 regarded merely as one state of Scenedesmus obliquus, the two 

 species of Dactylococcus mentioned above fit in all details Nageli's 

 original description of this genus, and hence Dactylococcus, Nag., 

 must be retained. 



Eecently, Grobety (in Bull. Soc. Bot. Geneve, 2nd ser. vol. 1, 

 1909, p. 357) has instituted the name " Ourococcus" for Dactylococcus 

 bicaudatus. This name is not only quite unnecessary, but was used 

 in 1845 by Hassal for his first subgenus of DLaiinatococcus, Ag., and 

 was corrupted by Kiitzing into " Urococcus." Hence it is in the 

 highest degree improper to use the name Ourococcus again for a 

 genus of green algae. 



103. Ankistrodesmus convolutus, Corda. 



Angola. Very abundant in the water-conduit and water-tank of 

 the cable-station at Mossamedes. 



This interesting species was in great abundance. The peculiar 

 spiral twist possessed by the cells causes considerable variation in 

 form according to the position of the individual. One pole fre- 

 quently appears rounded when the other is acutely pointed. 

 (Figs. 5-13). 



104. Cazlastrum sphcericum, Nag. 



Karoo. In sulphureous spring at Pappekuil ; 2.12.08. 



Family HYDRODICTYACE.F]. 



105. Pediastrum Boryanum, (Turp.) Menegh. 

 Karoo. With the preceding species. 



106. Pediastrum Pearsoni, G. S. West, sp. n. 



P. ccenobiis compactis, ellipsoideis in ambitu, sine lacunis, e cellulis 

 8 (2 centralibus et 6 marginalibus) vel 15 (5 centralibus et 10 mar- 

 ginalibus) formatis ; cellulis centralibus plus minusve irregulariter 

 pentagonis ; cellulis marginalibus subhexagonis, margine exteriori 

 angulari-rotundato ; cellula marginali unaquaque cum processibus 

 distantibus brevibus (2-4-6^ longis) binis, delicatulis et subcapitals, 

 oblique dispositis ; membrana cellularum firma et saspe subcrassa, 

 minute scrobiculata ; chromatophora unaquaque cum pyrenoidibus 

 singulis vel binis. 



