FRESHWATER ALG^. 47 



Genus Coscinodiscus Ehrenb. 



68. Coscinodiscus decipiens. 



(PI. Ill, fig. 151.) 



Coscinodiscus decipiens Grun., Diat. Franz Josefs Land, Denkschr. Ak. Wiss. Wien, xlviii. (1884), p. 85 ; 

 Van Heurck, Synops. Diat. Belg. (1880-85), PI. XCI., fig. 10. 



Diam. valv. = 1 8 /x,. 



Hob. — Pond some distance beliind hut, Cape Adare, January 9th, 1902 (isolated). 



Tlie specimens agreed well with Van Heurck's figure. In the central part of the 

 valve the punctse are large and widely separated, but they gradually become smaller 

 and more densely crowded towards the edge. The margin bears twelve short spines, 

 symmetrically arranged. The valves are markedly convex. 



69. Coscinodiscus lacustris. 



Coscinodiscus lacustris Grun., op. cit., p. 33, PI. D, fig. 300 ; Van Heurck, op. cit., p. 218, Suppl. PL C, 

 fig. 42. 



Diam. valv. = 30 ju,. 



Hab. — Pond some distance behind hut. Cape Adare, January 9th, 1902 (isolated). 



70. Coscinodiscus griseus. 



Var. GALLAPAGENSIS. 



Coscinodiscus griseus Greville, Quart. Joui-n. Micr. Sc. (1863), p. 230, Tab. IX., fig. 7 ; var. gdllapagensis 

 Grun. in Van Heurck, op. cit., PI. OXXXII., fig. 1. 



Diam. valv. = 57 fi. 



Hab. — Pond some distance behind hut, Cape Adare, January 9th, 1902 (isolated). 



Unfortunately only a single specimen of this form was seen, and that was lost 

 before it was drawn. AH attempts to find further specimens proved unsuccessful. 

 The single valve seen, however, agreed in every respect with Van Heurck's figure, and 

 I feel convinced that the determination is correct. 



Genus Cyclotella Kiitz. 

 71. Cyclotella operculata. 

 (Plate III, fig. 150.) 

 Cyclotella operculata Kiifcz., Bacill. (1844), p. 50, Tab. I., fig. 1 ; Van Heurck, op. cit., PL XCIIL, fig. 22. 



Diam. valv. = 20-38 //,. 



Ilab. — Pond some distance behind hut, Cape Adare, January 9th, 1902 (isolated). 



I have seen too few specimens of this form to feel sure of its determination. 

 The central region of the valve was in part quite without markings of any kind, in part 

 provided with irregular granulation, much as in West's figure (Brit. Freshw. Alg. (1904), 

 p. 277, fig. 127, b). 



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