280 ^- ''• Osti:ni-i;li). 



34. Fragilaria cylindrus (iruiiow, Dial. v. Franz Josefs Land, 

 1884, p. 5"), pi. 2, lig. 13; Gran, Bihliollu'ca Botanica, Heft 42, 1897, 

 p. 20, pi. 1, figs. 4—;"); Nord. Plankton, XIX, 1905, j). 11.'); Jørgensen, 

 Bergens Museums Skrifter, 190.'), p. 102, pi. (i, fig. 9. 



This species resembles the foregoing one very much, and it is 

 only possible to distinguish them when the ignified frustules are seen in 

 valvar view. Hence it may be that some of the records of F. oceanica 

 include this species of which I have seen sure specimens only in 

 one sample from Danmarks Havn, July 1908. 



Distrib. Arctic ncritic species of nljoiit the same (listiihulion as the 

 loretjoinif, l)iil ol'ten overseen. 



Thalasslothrix Cleve et Grun., 1880. 



35. Thalassiothrix longissima Cleve et Grun., K. Svenska Vet. 

 Akad. Handl., Bd. 17, No. 2, 1880, p. 108; G. Karsten, Wiss. Meeres- 

 unters., Abt. Kiel, N. F., Bd. 4, 1899, p. 28, fig. 11; Gran, Nord. Plank- 

 ton, XIX, 1905, p. 116; Synedra thalassiothrix Cleve, Bih. K. Svenska 

 Vet. Akad. Handl., Bd. 1, No. 13, 1873, p. 22, pi. 4, fig. 24. 



Only a single specimen found in a sample from the pack-ice in 

 Aug. 1906. 



Distril). Northern oceanic species, often occurrinf^ in <*reat (|iiantities, 

 e. 1^. in I^cnniark Strait and Irmin<>cr Sea. 



Achiiaiithes Bory, 1822. 



36. Achnanthes tæniata Grun. in Cleve et Grunow, K. Svenska 

 Vet. Akad. Handl., Bd. 17, No. 2, 1880, p. 22, pi. 1, fig. 5; Gran, Bi- 

 bliotheca Botanica, Heft 42, 1897, p. 9, pi. 1. fig. 10; Nord. Plankton, 

 XIX, 1905, p. 122, fig. 165; Jørgensen, Bergens Museums Skrifter, 1905, 

 p. 105, pi. 8, fig. 27. 



As Gran (1905, 1. c, in nota) has pointed out, Grunow's and 

 Jorgensen's figures represent chains with resting spores, wdiile in 

 Gran's two quoted papers we find the normal vegetative chains. 



Found in three samples from Danmarks Havn (Aug. 1907 and 

 July 1908) and, with resting spores, in one sample from the pack- 

 ice (July 1908). Perhaps overseen in other samples, as it resembles 

 Fragilaria oceanica and Navicula septentrionalis very much. 



Distrib. Arctic neritic species known from the Arctic Sea and the 

 inner Baltic (in spring). 



Navicula Bory, 1826. 



37. Navicula septentrionalis (Grun.) Gran,Bibliotheca Botanica, 

 1897, Heft 42, p. 9; Nord. Plankton, XIX, 1905, p. 124, fig. 167; Stau- 

 roneis septentrionalis Grunow, Diat. v. Franz Josefs Land, 1884, p. 105, 



