280 с. H. Ostenfeld. 



34. Fragilaria cylindrus Grunow, Diat. v. Franz Josefs Land, 

 1884, p. 55, pi. 2, fig. 13; Gran, Bibliotheca Botanica, Heft 42, 1897, 

 p. 20, pi. 1, figs. 4— 5; Nord. Plankton, XIX, 1905, p. 115; Jørgensen, 

 Bergens Museums Skrifter, 1905, p. 102, pi. 6, 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. 



Di strib. Arctic neritic species of atiout the same distribution as the 

 foregoing, but often overseen. 



Thalassiothrix Cieve 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. 



D i strib. Northern oceanic species, often occurring in great quantities, 

 e. g. in Denmark Strait and Irminger 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 

 Jørgensen's figures represent chains with resting spores, while 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 Naviciila septentrionalis very much. 



D ist rib. 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, 



