590 



//. viridis and has not the deep green ehromatophores, besides it 

 occurs from July to December, while //. viridis is to be found in 

 spring; further, I have found a spherical organism of about the 

 same dimensions with tetraedric division-stages and referred it with 

 hesitation to this species. 



Jorge nsen (1. c. p. 46) has also mentioned a Halosphaera as 

 H. minor. But now Gran has examined the Halosphaerae of the 

 Norwegian Sea of the last years and his opinion is that they all 

 belong to the same species. According to him the development 

 is as ibllows: — from August to April — May Halosphaera occurs 

 in the Norwegian Sea; the cells are during the first months small 

 (corresponding to H. minor Ostf.), but increase by and by until 

 the spring when they are 236 — 476 fi in diameter (H. viridis); in 

 the meanwhile the number of nuclei, which to begin with was 

 one, has become numerous; then the organisms disappear sud- 

 denly, and from May to August none are to be found. Gran sup- 

 poses that they produce zoospores but the latter cannot be caught 

 in the net. He says that he does not know if the North Atlantic 

 Halosphaera is the same as in the Mediterranean, as Jorge nsen 

 has seen zoospores with more than two flagella. But I think that 

 Gran is right in considering our form to be H. viridis. 



It is common in the plankton from the Færoes, and begins to ap- 

 pear in September — October and disappears in March— April; it often 

 predominates from November to January; temperature 5°— 10° C. — 

 Temperate, oceanic species. [See tables.] 



II. PACHYSPHAERA Ostenfeld, 1899. 



93. P. pelagica Ostf., Iagttagelser, etc, 1899, p. 52. 



This little-known organism which appears to be a resting stage, 

 has been found sparingly in samples from January — April, July and 

 October— November. Seems to be of temperate-Atlantic origin. 



II. NOTES ON THE PLANKTON. 



In his last and excellent paper on the Plankton of the Norwegian 

 Sea Gran points out that two methods may be employed for classi- 

 fying the plankton, viz. one may either consider the associations 

 of such species as often occur together and form a plankton of a 

 peculiar character as unities, or treat the single species as unilies, 



