563 



II. THALASSIOSIRA Cleve, 1873. 



2. T. Nordenskioldii Cleve, Ard. Sea, 1873, p. 6, PL II, lig. 1; 

 Van Heurck, Synopsis, PI. 83, fig. 9; Gran, Protophyta, 1897, p. 28, 

 PI. IV, lig. 59; Gran, Bemerk., Nyt Magazin f. Naturv., 1900, p. 116. 



This species most frequently accompanies T. gravida, bul il is more 

 particularly arctic. 



Found from March to August und reaches its maximum in March 

 Mav and in 1902 it had a secondary maximum in August, hul il is 

 not so common ;is T. gravida. See tables. 



3. T. gelatinosa Hensen, V" Ber. der Konim. /ur Unters. d. 



deutsch. Meere in Kiel, 18.S7, p. 87; Gran, Bemerk., 1900, p. 110: 



Coscinodiscus excentricus, var. catenata Gran, Protophyta, 1897, p. 30. 



A temperate, oeritic species, which is often confounded with Cosci- 

 nodiscus excentricus and is really very difficult to distinguish Ironi it. 

 when the thin central mucilaginous thread is nol present. It is a 

 winter- l'orm. and is found from November to April and reaches its 

 maximum in March. Optimum ol' temperature 1° -7 "C. See lables. 



4. T. gravida Cleve, Baff. Bay, Bih. t. K. Svenska Vel. Akad. 

 Handl. Bd. 22, Aid. III, No. 4, 1896, p. 12, PI. 2, ligs. 14, 15, 10; 

 Gran, Protophyta, Norw. North-Atl. Expedition , 24, 1897, p. 28, 

 PI. IV, ligs. 57, 58; Gran, Bemerk., 1900, p. 115. 



A horeal- arctic, neritie form, met with along the eoasls of the 

 Northern Atlantic Ocean from the North Sea norlhwards in the Arctic 

 Ocean. Around the Færoes it occurs from March to August and but 

 rarely in September— November. It reaches its maximum in March- 

 Mav. but in 1898 it was also rather common in June— July and in 

 1002 in August. Rather indifferent with regard to salinity and tempe- 

 rature (about 5°— 11° C). [See lables.] 



5. T. subtilis (Ostf.) Gran, Bemerk., 1900, p. 117; Podosira (7) 

 subtilis Ostenfeld, Iagttagelser, 1899, p. 55; 1900, p. 54. 



I found a small Diatom in plankton from the North Atlantic 

 Ocean, collected in 1898, which I referred with hesitation to the 

 genus Podosira. Gran found the same diatom later on and he 

 refers it to the genus Thalassiosira because it has one connecting 

 ring (copula) to each valve besides the connecting band (pleura); he 

 does so somewhat doubtfully as neither he, nor I, have seen any 

 mucilaginous thread as connection between the cells, the latter being 

 merely embedded in an amorphous mucilage. I give a lignre of a 

 colony of cells embedded in the mucilage; afler treatment with 

 safranine the mucilage occasionally hecame somewhat striated. 



The cells are placed without order, sorae in valvar view, other in 

 girdle view, and it is impossible to know the reciprocal ages of the dif- 



Botany <>r Uie Færdes. !i(> 



