583 



78. P. depressum Bailey, Smithson Contrib. to Knowledge, II, 8, 



Washington 1850, p. 12, ligs. 33— 34. 



A very characteristic species ol' boreal, oceanic origin; rather cora- 

 mon around the Færoes and found during most of the months. fSee tahles.] 



79. P. oceanicum Vanhoffen, (ironiand Exped. d. Gesellsch. f. 



Erdkunde zu Berlin, Bd. II, 1, 1897, PI. 5, lig. 2. 



Temperate, oceanic species which is rare along the Færoes; found 

 in January, .lune and October, bul in a few specimens. 



VIII. CERATIUM Schrank, 1793. 



The species of this genus are the most important plankton-forms 

 of the Peridiniaceae; the northern forms have been treated by al- 

 most all the authors who have written about the plankton of the 

 North Atlantic Ocean and its tributaries, vi/. Schull, Vanhoffen, 

 Cleve, Jorgensen, Gran and the author of the present paper. 



Subgen. 1, EUCERATIUM Gran. 



Sectio Tripos. Antapical- horns elosed at the distal end; lists 

 of Ihe horns without spines. 



80. C. tripos (O. F. Miill.) Nitzsch., Syn. C. tripos, var. baltica 

 Schutt, Pflanzenleben d. Hochsee, fig. 20 IV a, lig. 35 I. 



Fig. 132. Fig. 133. 



Fig. 132. Ceralium tripos (O. F. Miill.) Nitzsch., f. atlantica n. f., a specimen with longer and more 

 diverging horns ( lvj /i)- — Fig. 133. Ceratlum tripos O. I«". Miill.) Nitzsch., f. atlantica n. f., a specimen 

 with rather short and only slightly diverging horns ( L,0 /i). 



A form of this species is common in the plankton around the Færoes 

 and also in the Norlh Atlantic Ocean, especially in its eastern part. It 

 is a temperate species which reaches its maximum in August— October 

 along the Færoes. [See tables.] 



