8 O A RO LIM E \j B E (i A A B D. 



1896 Ch. bottnicum Cleve, at Aurivillius, p. 14, pl. 1. 



1897 a Ch. biconcavum Gran, p. 27, pl. 3, f. 46. 

 1897 a Ch. Wighami Gran, p. 27. 



1901 Levander, p. 6, 13. 



1908 Gran, p. 88. 



1910 Meunier, p. 244, pl. 27, f. 26. 



1913 Meunier, p. 42, pl. 6, f. 32—34. 



Chaetoceras Wighami was fourni at every station occurring both as very thin-walled 

 cells and as resting-spores. The cells were either observed singly or in short chains 

 consisting of very few cells. The resting-spores lying one in each cell were decorated 

 on both valves with fine spines, which were easily seen on the larger cells, but were 

 very indistinct on the smaller ones. 



The breadth of the chains was 6 — 17 u, the greater nuinber of the resting-spores 

 however not exceeding 10 «. 



At station F 41 Ch. Wighami occurred rather numerously being hère without 

 resting-spores, while only a few straggling cells or spores were fourni at the stations 

 F 50, F 61, F 74 and F 30. At station F 23 the resting-spores were dominating with 

 maximal nuinber at the depth of 30 mètres. At this station it is still fairly nnmerous. 

 but. no doubt in regression. 



Coscinodiscus lacustris Grun. 



(Fig. 5.) 



1884 Grunow, p. 85, p]. 4. f. 30— 33. 



1899 Van Heurck. p. 525. 



1910 Meunier, p. 274, pl. 30, f. 33—34. 



The undulated valve of Coscinodiscus lacustris having one excentric concavity and 

 one excentric convexity can be dissolved into narrow sectors consisting of 3 (2 — 4) rows 

 of pores. The sectors are separated by thickened lists just inside the margin, while 

 the very border of the valve is very delicately radially striped. 



The size was highly varied, the diameter ranging between 20 u and 70 ;/. 



In spite of Coscinodiscus lacustris being a very characteristic species, when it was 

 deprived of its contents by intense heating, it was rather difficult to détermine this 

 species, when it was counted, as the contents were of a dense black colour. When 

 looking at the valve it was particularly difficult to distinguish the small cells of this 

 species from those of Thalassiosira baltica. On that account the numbers put down in 

 the tables concerning thèse two species are not quite exact. Under Coscinodiscus lacustris 

 are noted every cell, which lias been determined with certainty as this diatom, while 

 those, of which the identification is uncertain, are counted as Thalassiosira baltica, this 

 species on closer examination appearing to be the dominating one. 



Tom. XLV1II. 



