Protistplankton. 



liucly in my niatciinl. \rt. I linvr the impii'ssioii that it is only 

 a (luestioii of dirt'crciit loniis. not of (iilt'crcnt spfcics. 



When the outsido siioll is wanting — 1 look ujjon such forms 

 a-s younir specimens — I am, however, ([uite unable, at present, at 

 any rate, to decide whether tiie specimen l)clou<;s to tlic one or the 

 other of the species above mentioned, (t'fr. pi. VI II. f. :i2, a, b). 



H. cnthaviinthiim jrnic. 

 (I'l. VIII. f. :!"■). 



1 will only add a (^^w remarks to the detailed description given 

 1. c. (,l(')U(iKxsi:N L. 1)1, p. 'y2). 



This species diHers from tlie foilnwiiiL'- in liavinu- a delicate 

 outer shell with comparatively narrow walls hot ween the pores and 

 no byspines. 



As in the followiui;- species, the pores on the outer shell are 

 different in size, from 6 — 10 |i, most of them being S |i., although 

 they arc not strikingly unlike. 



The pores of the middle shell in both species arc also alike, 

 there is a slight variation in the size of them on the same shell, 

 they average 4 — .5 \i (seldom as little as 3 or as much as 7). The 

 pores on the two outer shells are about equal in number on 

 the radius. But the inmost shell differs considerably in this re- 

 spect, the pores here being comparatively much larger and conse- 

 quently much fewer in uumbei-. 



On young specimens, where only the two inner shells are de- 

 veloped, one may often see transverse processus on the radial spines 

 where the outer shell is found later on, these processus forming the 

 intermediate walls of those pores in the outer shell wdiich are 

 situated nearest to the main spines. On still younger specimens, 

 however, these processus are also wanting. 



Such forms (cfr. pi. VIU, f. 32) may easily be mistaken for 

 species of the genus Hexnlonche. If one considers the coincidence 

 in dimensions and construction of the inner shells of Hexacontium 

 enthacantlutm and H. pitch ydennum, it would, however, seem most 

 reasonable to look upon them as being forms of these species. 



The outer shell varies in its development from very thin to 

 moderately thick. The pores on the thicker shells seem to be 

 rounder and to have wider walls, which are more plainly widened 

 out in the corners. 



I have very rarely seen specimens witii a trace of byspines 

 (conically heightened parts) in the corners between the pores. 

 Tiiese traces of byspines appear, however, to denote that the limit 

 in the direction of H. iMchijdannum is not certain. The common 

 name ought in this case to be H. pitch ijih-rmmn. which would then 

 represent the grown form. 



The number of the main spines is usually fi, and sometimes 7, 

 but very seldom more. These spines are usually about equal in 

 breadth inside as well as outside the outer ball. 



Ocean forms, of which I have seen a few, seem to diverge 

 somewhat (both in this and the following species). The specimen 

 illustrated pi. VIII f. 30 for instance, had a rather strong outer 

 shell with main spines, which, as is the case with H. pachy- 

 dei-miim, were considerably narrower inside the shell than outside. 

 The inmost shell too was more solid than usual, and had compara- 

 tively more pores and with stronger walls (clr. tig. 30 b.). 



The dimensions of outer and middle shells on 7 individuals (the 

 6 from the west coast of Norway): 



Thus it will be seen that llir dianwlrr oftlH- middl.' shell varies 

 remarkably little, while that of the outcsr one varies considerably. 



Rare, in deep water samples, always in small numbers. 



Distribtttion : Temperate oceanic form, which with us is only 

 found in deep water, especially at a depth of 300 m. or more. 

 Somewhat more frequent on the west coast of Norway. Also known 

 from scattered spots in the sea beyond the coast of Noi'way and 

 from the Faeroe and Shetland Isles northwards. 



H. pachyderniiini JiJi»;. 

 (PI. VIII, i. :il). 



The byspines on the outer shell vary considerably in length. 

 They are found in all corners where the pores meet, so that each 

 pore is surrounded by several byspines (generally .5 or 0). 



The pores on the outer shell are more or less round, the inter- 

 mediate walls being on the whole broader than in the preceding 

 species, answering to the development of the outer shell which is 

 altogether stronger in this species. This shell is especially thick. 



The length of the main spines varies considerably. 



The byspines on the middle shell are little conspicuous, and may 

 be easily overlooked (as in the case of the preceding species). 



The innermost shell is here seen less clearly than in H. enth- 

 acanthum, unless the thick outer shell be removed. One may, 

 therefore, easily mistake this species for a Hexalonche. by over- 

 looking the inside ball. I have, however, repeatedly convinced 

 myself on breaking the outer shells, that it is alwayå present. Its 

 construction is the same as in the preceding species. 



No important difference in dimensions between this species and 

 the precedmg one seems to be found, and this is a very important 

 factor when considering the question as to whether these supposed 

 species arc specifically different, or only constitute different forms 

 of one and the same species. Here too the outer shell varies in 

 size, but the middle and inmost ones are remarkably uniform in 

 this respect and resemble those of H. enthacanthum. 



The ocean forms, however, appear to diverge essentially. I 

 have not had an opportunity, though, of studying them more thor- 

 oughly in richer material, so that I cannot yet give a definite opi- 

 nion as to the probability of separating new species. This, however, 

 does not seem unlikely. 



For such a strongly developed ocean form from the sea beyond 

 Sondmore (in February 1901, S/S Michael Sars, a sample kindly 

 given me by Dr. Gran) was found: 



Strong, long main spines (most of them broken off"). Numer- 

 ous byspines (4—6 round each pore), long, needle shaped, 40 \i. 

 long (nearly *ii of the radius of the outer shell). Outer shell very 

 thickwalled (6—7 |jl thick), pores almost even, + 8 |j., very broad- 

 walled, round, a little broader than the walls. 7 main spines, much 

 narower between the outer shells than outside the outmost one. 

 The diameter of the three balls 108 is 39, 19. 



Occurred like the preceding species rather rarely and sparsely 

 in deep water samples, though perhaps somewhat more frequently. 

 As a rule it is found in deep water samples from such outer pla- 



