12 P. T. CLEVE, PLANKTON-RESEARCHES. 



This association of forms has a very great reseinblance to the plankton found in 

 April in the Skagerak. If the southern forms be omitted not less than 64 percent of 

 the northern forms occurred in April in the Skagerak. I can scarcely wish for a better 

 confirmation of my hypothesis that the plankton that occurs in the Skagerak in the 

 early spring is derived from the western Atlantic. 



The samples collected by »Heimdal» at 65° — 67° N. 6° — 11°W. were on the whole 

 very poor and contained chiefly arctic and boreal forms, two only, Oithona similis and 

 Glohiqerina being of southern origin. The most interesting forms were Calanus hyper- 

 boreus and Oncoea conifera. 



The »Heimdal» collections at 67°— 68° N. 1°— 13° E. prove that the plankton west 

 of Norway belonged to the tripos-iy^e, but containing Halosphcera, and west thereof to 

 chceto- and ij-^c/io-plankton. As Mr. Gran has already pointed out the plankton at 13° — 8° E. 

 corresponds with the plankton at 61° N. 4°— 1° E., that at 68°N. 3°— 6°E. with the 

 plankton at 62° N. 0°— 1° W. and 67° N. 1° E. with 63° N. 2° E. 



The state of the Northern Atlantic in May 1901 is thus very clearly shown by 

 the researches of Mr. Gran. West of Norway there predominated <r^pos-plankton at least 

 for 5 degrees, as also in the Skagerak. West of the Norwegian triposregion to the Färöes 

 Ave meet with more or less abundant chceto-Tglaukton, thus the same kind as occurred 

 during April in the Skagerak. 



June 1901. 



Only two samples were collected the 3d and 14th at Måseskär but none at Väderö- 

 boda. The plankton was a typical ^npos-plankton. Of the species noted 28 remained 

 from May. Only 6 new forms, all southern neritic, occurred very sparingly. Two addi- 

 tional forms may be classed as northern neritic forms, but occurred very sparingly. The 

 total number was thus relatively small. 



July 1901. 



Samples were collected at Väderöboda only, but throughout the month. The plank- 

 ton was till about the 20th tripos-plsmkton, but from the date named J^V/?/m^^s-plankton 

 became abundant owing to the development of Chcetoceros curvisetus and Schiittii. 



The forms noted during June and July can be classified as follows. 



Remnants from ^^ ^ ^ i 



May New. Total. 



Southern oceanic 9 3 I ^4. 



Southern neritic 3 9 1 



Northern oceanic 10 O 1 q, 



Northern neritic 9 2 I 



August 1901. 



During this month the North Sea was explored by steamers from Göteborg to 

 Hamburg, Antwerp, Hull, Edinburgh and Glasgow. The Skagerak was also explored 



