Protistplanklon. 



ir 



l>r.> ■■■> 4>iiiiii]i flt')i:tns Jintd. 



JoKtiEXSEX L. 91, p. 58. 



This species, wiicu fully (levcloped, is very easily reeot-nized 

 by its liranched byspincs on the outside shell. 



The outside shell is strou.iiiy deYj?loped, thick' walled, diameter 

 _:_ s.') |i. The poi-es are roundish with broad intermediate walls, 

 unevenly developed, thoui^h not so nnich so as in Cliromi/echinu.i 

 bi/r<:iilis. on an avera,<rc about the same size or perhaps most of 

 them a little smaller. 



The two inner shells seem in all important respects to answer 

 to those of the following species, Chromi/echimis boredis. Still, I 

 nnist call attention to the fact that I have had very little chance 

 of examiniuii- them more tliorouijiily. as the species occurs so 

 spai'sely. 



The number of the main spines seems to vary (?) from about 

 lo up to about 20. The largest are beautifully developed, long, 

 slendei' and always branchless, a few of the smaller ones seem, 

 on the contrary, occasionally to have a single needle shaped side 

 bi-anch, like the corresponding one in Chromyechinus borealis. 



Of byspines there are some resembling the main spines, only 

 smaller and especially narrower. From these .3-edged spines there 

 seems to be every transition to numerous narrow needle shaped ones 

 without distinct edges. 



^lost of the byspines, especially the narrow ones, carry in 

 tlieii- upper halves from 1 — i obliquely diverging narrow branches, 

 some of these again carrying a similar, but shorter, side branch. 



There seems to be a regular transition from the more delicate 

 radial spines to the more sti'ongly developed, 8-edged and branch- 

 less, byspines. 



It is, however, as above mentioned, probably not quite certain 

 that the previously mentioned Ecliinomma-f orms with long, slen- 

 der main spines and byspines, should all be included in this spe- 

 cies. These forms occur, with us, much nioix- frequently than the 

 fully developed Drymyommu clcfinus. 



Rare and scarce, only found at a few places in 1899: Sea 

 otf GaukværO, "A, 0—700 m., Senjen, 'Vi, 0—130 m., the Vest 

 Fioid, V-.s 0—200 m.. Skroven, V=, 350—300 m.. the Tys Fiord I, 

 ^%, 0—700 m. 



DiMr'ibutwii : Very rare also on the west coast of Norway, 

 only in deep water. Also kn()\\n from the Norwegian Ocean oif 

 Sundmore and from the Vest Fioi-d. Feb. 1901. (Cfr. Guan L. 70, 

 p. 150—151). 



Chroni:»'ecliinn!>> borealis (Cl.) 

 tPI. VIII. f. 3.t: pi. IX. fig. 3()— 37). 



Actinomma boreale Cl. L. 30, p. 20, pi. 1, f. 5 c (vix a, b). 



Chromyomvm boreale (Cl.) .Turu. L. 91, p. 59. 



This remarkable species is ea.sily recognized by its four shells, 

 of which the outside one is exceedingly delicate and very differently 

 developed. This outside shell is very often wanting, but there are 

 usually — as before mentioned — indications of it in tlie trans- 

 verse processus on the radial spines. 



On the outside shell there are — but only i-arely in the ma- 

 terial which I have examined — nai'row bysjiines, few in number, 

 -which most often form more oi- less oblifiuely (not straii'Titly ra- 



dially) i)roti-uding extensions of the walls between the pores. They 

 may also sometimes be seen as bristle-shaped branches extending 

 obliquely out tVom the main spines. They arc^ thus not radial by- 

 spines, althoui;h they have uii(l(iiii)tc(||y the same bioloL-ical value 

 as these. 



On account of these spines, it will. I think, be most correct 

 to enter the species as a Cliraniyrrlninis, es]iecially as, on the shell 

 next to the outside one. thei'e are both main spines and byspincs 

 (both having the same appearrancc) in the same sense as in Eclii- 

 nomma trhiacrium. 



It is quite remarkable to what variations this species is sub- 

 jected, even in the matter of dimensions. 1 have found the follow- 

 ing dimensions on the three outer shells, for specimens: 



It will be seen that the dimensions of the shell next to the 

 inmost one diller only a little from the corresponding ones in Hex- 

 acontiuvi enthacanthum, H. pachydermum and Ech'inomma leptocUr- 

 iiium (as well as in E. trinacrium and Drymyomma elcynns). The 

 third shell too corresponds, on the whole, well to the third one in 

 the species mentioned. 



This is a very interesting phenomenon, seeming to indicate a 

 development of all these forms from a common, comparatively young, 

 principal form, the balls being probably formed centrifugally, at 

 any rate, after the second. It may, on the other hand, perhaps 

 be the case that the less developed inmost shell is formed later, 

 centripetally. I mean that I have seen traces which lead me to 

 conclude that its connection with the second ball is not merely a 

 prolongation of the radial spines. 



In this species, it seems to be possible to distinguish between 

 two series of forms, which in their extreme forms are so different 

 that one would not hesitate to class them as distinct species, if 

 there were not so many variations within each series that as yet 

 it does not seem able to fix any certain limit. It is not unlikely 

 that really here exist several closely allied .species. 



The one series of forms (cfr. pi. VIII, f. 35) has shorter broader 

 spines, not very different in development, on the whole very similar 

 to those of Ech'momma trinacrium Hck. The outer shell is very 

 delicate, closed. 



The othei- series has longer, moi'e slendei" spines, varyini;' con- 

 siderably in size. The outer shell is of firmer construction, and 

 always seems to be open on one side (not complete). Here the 

 radial spines and the byspines arc particularly long, and this cir- 

 cumstance together with the large hole in the outer shell causes a 

 foreign appearance, something like in certain .species belonging to 

 the Nassellaria and Phacodaria groups. 



On strongly developed forms of this second series, there are 

 also sometimes seen „ false" byspincs, as described above, at any 

 rate in the form of side branches on the largest radial spines on 

 the open side of the outer shell. 



On those forms too where the outer ball is closed, there often 

 seems, however, to be a comparatively .strong development of the 

 spines on one side of the shell. 



