570 



A temperate, oceanic form, which occurs sparing]}' all thc year 

 round in the plankton of the Færoes, in July only it is predominant 

 but not every year. Optimum of temperature 9°— 11 °C, [See tables]. 



BIDDULPHIEAE. 

 XIII. CERATAULINA Perag, 1892. 



28. C. Bergonii Perag., Monogr. Rhiz., 1892, p. 103, PI. I, 

 ligs. 15, 16. Zygoceros (?) pelagicum Cleve, Kanonbaaden Hauch's 

 Togter, p. 54 (1889), with fig. 



A temperate, neritic species which occurs sparingly in 



The specimens from the Færoes are always large 

 and short, resembling Peragallo's figures and nol 

 those by Schutt in Engler & Prantl. nor those by 

 Cleve (1. c); I should think that the latter (the Katle- 

 gat and Baltic form) is somi 

 Allantic and North Sea form. 



the plankton from most of the months (February— December). 

 li %l% !« [See lables. 



S 



Fig. 126. Ceratau- 

 lina Bergonii 



h. pemg. a ceii g a t and Baltic form) is somewhat difJerent from the 



of the large and 

 short form ""' , I. 



XIV. BIDDULPHIA Gray, 1831. 



29. B. aurita (Lyngbye) Bréb. 



A rommon littoral form of boreal-arctic origin which occurs in the 

 plankton from February— April only; sometimes common. Optimum of 

 temperature about 6° C. [See tables.] 



CHAETOCEREAE. 

 XV. BACTERIASTHUM Shadb., 1853. 



30. B. delicatulum Cleve, Fish. Board for Scolland, 1897, 



p. 298, hg. 15. 



Of tliis little species, which belongs to the temperate North Atlantic 

 Ocean, I once observed a chain in a sample from Thorshavn taken in 

 November. 



XVI. CHAETOCFRAS Ehbg., 1844. 



The genus Chaetoceras has of all the plankton-genera of 

 diatoms almost the greatest number of species; I think that more 

 llian 100 species are described. Thc only attempt lowards dividing 

 Ibis large genus into natura! sections has been made by Gran, who 

 founded the hvo subgenera Phaeoceras and Hyalochaete relativelv on 



