KOPOID AND SWEZY: UNAKMORED DINOFLAGELLATA 397 



waters, or to the more northerly waters which receive wann currents, vet the 

 significance of this fact is greatly modified by its seasonal distribution. Its 

 occurrence in its more northerly range is quite as frequent in the colder as in 

 the warmer months. Thus it has been found in the North Sea and the Skage- 

 rack from September to January (Aurivillius, 1896-98) and along the coast of 

 Norway in November and December (Jorgensen, 1899). 



PoJijkrikos, unlike most of the Gymnodiniidae, is fairly well able to with- 

 stand the destructive influences of fixing fluids, and is occasionally found in 

 preserved material. In examinations of the plankton hauls made off San Diego 

 for several years and covering every month of the year specunens of Polijkrikos 

 have been found only in the hauls made during June and July of different 

 years. In the sununer of 1917 it was present from June 26 to August 22, though 

 never abundant. It has been found in San Francisco Bay in October and 

 November. 



Historical Discussion 



The history of Pohjknkos has been a varied one, owing to its peculiar 

 structure, which, in the earlier descriptions of it, was but imperfectly under- 

 stood and served to obscure its relationships. The organism was first described 

 l)y Ouljanin (1868) as a pelagic turbellarian larva and later by Biitschli (1873) 

 as a eiliate infusorian, Poh/krikos schwartzi. In 1881& Bergli referred it to 

 the Cilioflagellata, added another species, P. auricidaria, and figured cilia on 

 the transverse furrows. Later Pouehet (1883, 1887) accepted this allocation, 

 without, however, figuring the cilia. Biitschli (1885) in his monograph on the 

 Dinoflagellata recognized the dinoflagellate character of this organism and 

 omitted tbe cilia in his figures, substituting flagella therefor. He placed it in 

 a se])arate family, Polydinidae. Schiitt, both in his systematic monograph of 

 the Peridiniales (1896) and in his report on the Peridiniales of the Plankton 

 Expedition (1895), omitted all reference to the genus. 



Delage and Herouard (1896) marked it off as a still more unusual form by 

 creating for it the order Polydinida with this genus as its sole representative. 

 Kofoid's (19076) work on this puzzling organism served to clear up many of 

 the obscure points in its structure with a resulting clearer elucidation of its 

 relationships. He placed it in the family Gjrtnnodinidae (= Gymnodiniidae) 

 without further isolation unless that family should be broken up into sulifnni- 

 ilies. A critical examination of an al)undance of material also indicated that 

 both Biitschli and Bergli were dealing with one and the same organism and 

 not with two distinct species. Our later work on Polykrikos confirms these 

 earlier observations (Kofoid, 19076), aud we therefore place Bergh's species 

 as a synonym of Biitschli 's P. schwartzi. 



The form figured by Kofoid ,was afterward separated from P. schu-artzi 

 by Chatton (1914c), as P. kofoidi. The specific distinctions on which he based 

 this separation are two in uuuibci', the first being the absence of nematocysts, 



