KONGL. SV. VET. AKADEMIENS HANDLINGAR. HAND 34. .V.O I. 17 



This species has bcen found in samples from the Indian ocean as well a9 from the 

 Atlantic, where it occurs in the tropical part, at least Ironi 21 S. to 17 N. Temperatun 

 23,8, mean of 43 obs., max. 28,3, min. 10. Salinity ■">"», "4, mean of 1" obs., max. 37, 

 min. 32,87. It belongs to desmo-plankton. 



Peridiiiiiim cxiguiini. N. Sp. 

 Plate VIII. Fig 5. 



This species is also nearly akin to P. divergens, bnt differs in the small size 

 (length 0,05 — 0,06, breadth 0,04 millim.), the coarse areolation, the serrated posterior horns 

 without basal teeth and in the obliqne girdle. 



I have found it in samples from the Azores (August 1898) and from the coast of 

 Portugal (June 1898). Temperaturs 21,2. Salinity 36,25. It belongs probably to styli- 

 plankton. 



Peridinium oceanicum Vaniiöffen. 

 Plate VII. Fig. 17, 18. 



In the »Peridineen der Planktonexpedition» (Pl. XIII, fig. 44) Schutt has figured, 

 as a variety of P. divergens, a common atlantic form, which Vanhöffen (Grönl. Exp., 

 Vol. II, 2 part, Pl. V, fig. 2) names P. oceanicum. The same form was, also in 1898, 

 named by Aurivillius (Kongl. Sv. Vet.-Akad. Handl., Vol. XXX, n:o 3, pag. 96) Perid. 

 div. var. obliqua. 



It is a very constant, easily recognised form, which I have seen in samples from 

 the Red Sea and the Indian ocean. It occurs in the Atlantic chiefly in the region of the 

 Azores and N. thereof, in the spring across the whole Atlantic, between 40° and 50° N., 

 whence it spreads, during the summer, towards Greenland, into the Irminger Sea and 

 across the Färöe Channel into the North Sea and the Skagerak. Temperature 12,9, mean 

 of 32 obs., max. 22, min. 3. Salinity 35,45, mean of 28 obs., max. 36,25, min. 34,i6. 

 (For the calculation of the means only such samples have been used as contained this 

 form in any abundance) It is a typical styli-plankton form. 



Peridinium pallidum Ostenf. 



Plate VII. Fig. 21, 22. 



Under the above name Ostenfeld (Iagttagelser över overfladvandets temperatur, 

 saltholdighed og plankton in 1898, pag. 60, 1899) has distinguished a form nearly relä .ted 

 to P. pellucidum, but with oblique posterior horns. 



It is an arctic form, that ranges between 39° and 79° N. Temperature 8,5, mean 

 of 45 obs., max. 19,4, min. 0. Salinity 34,87, mean of 45 obs., max. 35,97, min. 32,43. 

 It belongs to triého -plankton and to the northern nevitic plankton. 



K. Sv. Vet. Akad. Handl. Band 34. N:o 1. 3 



