KONfiL. SV. VKT. A!C,\nF,MIF.NS H A\'l)MNn AH. BAND 34. N:0 I. 17 



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

 Atlantic, where it occurs in the tropical part, at least from 21 S. to 47'' N. Temperature 

 23,8, mean of 4.") ohs., max. 28,:!, min. 10. Salinity 35,84, mean of 40 obs., max. .'i7,J8, 

 min. 32,87. It belongs to desino-plajikton. 



Peridiniiim exiguum. N. Sp. 

 Plate VIII. Fig 5. 



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

 (length 0,or. 0,or,, breadtli 0,04 millim.), the coarse areolation, the serrated posterior horns 

 without basal teeth and in the oblique girdle. 



I haA'e found it in samples from the Azoi'es (August 1898) and from the coast of 

 Portugal (rTune 1898). Tempei'ature 21,2. Salinity 36,25. It belongs probably to ntyli- 

 plankton. 



Peridinhim oceaiiicuiii Vanhoffen. 

 Plate VII. Fig. 17, 18. 



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

 as a variety of P. divergens, a common atlantic form, which Vanhoffen (Gronl. Exp., 

 Vol. II, 2 part, PI. V, fig. 2) names P. oceanictnn. 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. ohliqua. 



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 Faroe Channel into tlie North Sea and the Skagerak. Temperature 12,9, mean 

 of 82 obs., max. 22, min. 3. Salinity 35,45, mean of 28 obs., max. 36,25, rain. 34, le. 

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

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



Peridiniiim pallidum Ostenf. 

 Plate VII. Fig. 21, 22. 



Under the above name Ostenfeld (lagttagelser over overfladvandets temperatur, 

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

 to P. pelhicidum, but with oblirpie 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, a7, min. 32,43. 

 It belongs to trieho-plnnkfon and to the nortlirrn ncritic plnnkton. 



K. Sv. Vet. Aknil. lIuM.ll. liaml .14. N:n 1. 3 



