520 Annals of the South African Museum. 



spores (such forms being included as Pseudulothrix by Pascher, Stud, 

 ueb. d. Schwaermer einig. Suesswasseralgen, Bibl. Botan., Heft. 67, 

 1907, p. 106). Heering (Joe. cif.) includes this and other biciliate 

 species in the genus Horrnidium, a number of whose species are 

 terrestrial. He bases this on the fact, that these latter species of 

 Horrnidium likewise have biciliate macrozoospores, and on certain 

 other resemblances in cell- structure and mode of reproduction between 

 the two sets of forms. 



The specimens in samples 56 and 57 agree in habitat and characters 

 altogether with the figures and description given by Klercker and 

 Heering. The cell-wall is delicate ; the cells vary from a little longer 

 than broad to three times as long as broad, and are from 5 to 7' 5 \i in 

 diameter. The chloroplast is very characteristic, being a circular or 

 elliptical plate, according to the shape of the cell, and containing a 

 small, pale, central pyrenoid (c/. Fig. 12). It seems likely that the 

 elliptical shape of the chloroplast presages division. The extent of the 

 chloroplast is very variable ; sometimes it almost fills the cell, in other 

 cases only part of it. Curious knee-like bendings are not uncommon and 

 appear to mark stages in the splitting of the threads (Fig. 12, b-d). 



2. Horrnidium rivulare, Ivuetziug, Phycol. german., 1845, p. 192 ; 

 Heering, op. eit., p. 47, Fig. 56. (Syn. : Ulothrix rivularis, Kuetzing, 

 Spec. Alg.,' 1849, p. 346; Hormiscia hieronymi, Lemmermann, Zur 

 Algenfl. d. Kiesengebirges, Forschungsber a. d. Biol. Stat. Ploen, iv, 

 1896, p. 104). 



Sample 50 (Fig. 13) ; resting-stages in samples 22, 38, and 39 

 (Fig. 14). 



This is a more robust form than H. subtile, the diameter of the fila- 

 ments, in the present material, being 7-10 \i ; the cells are as long as 

 broad or up to twice as long. The walls are considerably thickened 

 (Fig. 13), even the septa being affected in some cases. There is a 

 faint constriction between the cells. The chloroplast is nearly always 

 circular (Fig. 13) and only occupies a small part of the length of the 

 cell, being situated either in the middle or near one end. The pyre- 

 noid is more prominent than in H. subtile. In many cases the chloro- 

 plast exhibits two lateral arms projecting from the circular main 

 portion on either side (Fig. 13, (f. c, d) ; all transitions from a purely 

 circular chloroplast (Fig. 13, b) to one showing pronounced arms can 

 be found. Knee-like bendings (Fig. 13, e) were not as frequent as in 

 the previous species. 



This and the preceding species, together with Horrnidium fluitans 

 ((.lay), Heering (Stichococcus fluitans, (-lay. Bull. Soc. Bot, d. France, xl, 



