Protistplanktou. 



129 



Only two pent- 

 ai;oiis witli a side 

 in common and 

 tlic opposite cor- 

 ners connected 

 throutrli a poly- 

 i!onal beam; long- 

 spines in tlie 

 cornel's 



Jlore or less 

 developed net- 

 work, formint;- a 

 conical cephalis, 

 open below .... 



Only the 4 main 

 spines with a ver- 

 ticil of 3 branches 

 ou each of them; 

 no or but few^ 

 connecting- ai'ches 

 developed 



Gunospha-ra. 



Pledacantha. 



Plagiacantha. 



VII C. 1. Plectoidea HcK. (Plagonitla and Plectanida). 



Plagiaeantlia arachnoides Clap. 



Jørgensen L. 91, p. 72. 



In a previous paper (Joegensen 1. c), 1 liave in detail de- 

 scribed the structure of this species and shown that, from this 

 structure, it would have to be classed as belonging to Haeckel's 

 genus Plafjiocarpa or — the form which is furnished with connecting 

 beams — to Perijjlecta Hck. At the same time too is mentioned that 

 this structure — as it is explained in the foregoing pages here — 

 is the ground type for a large series of forms. 



It is likely that still other species are included in the above 

 name. Haeckel's Plectophora aradmoides can, however, not be 

 distinguished from Plagiacimtha arachnoides. 



In the present material, this species was found only rarely 

 and in small numbers, generally in deep water samples, up to 50 

 ni., only exceptionally near the surface. Almost entirely absent 

 during the diatom inflow. 



Distribution: According to Cleve (L. 40, p. 180) a northern 

 form, belonging to Tricho- and Chætoplankton. Frequent on the 

 west coast of Norway, seems also there to be absent during the 

 diatom inflow. In August 1903, numerous between the Faeroe 

 and iShetland Isles and in the sea north of them, near the surface 

 (L. 18, 1903—1904, nr. 1). 



The species would thus seem to belong to the noi'thern part 

 of the Atlantic, and especially to be abundant in the North Sea 

 and north of Great Britain during the summer months. 



Canipjlafantiia n. ^^in. 



Has tile four pi'imary spines, D, L^., I^i and A, as well as 



the ventral, sagittal one, V. Tlie dorsal, sagittal one, D, is bent 

 strongly downwards. The lateral, basal spines, L and L[, are 



also bent downwards, beini;' as usual directed half forwards and 



half sideways (so as to be ventral lateral). The ventral, sagittal 

 spine is rather thin, almost straight, bent strongly downwards and 

 converges distinctly towards the dorsal, basal spine, 1). 



The principal ditt'ercnce between this and the previous genu.s 

 lies in the ventral, sagittal spine. 



The primary verticil of branches (cfr. the introductory remarks 

 under Xassclhtria) appears only on the apical spine, which is with- 

 out any other branches. 



C. cladophora .hmc. n. sp. 

 (PI. XII, tij,^ 47). 



The sagittal, basal spine is best developed, very strong-, long, 

 strongly bent, gradually narrowing ort" into a long fine point, like 

 all the stronger main spines and branches three-edged. One edge 

 is dorsal, the others lateral. On these three edges, there are strong, 

 expanded, narrow pointed branches, several in a row along the same 

 edge, rather scattered and not clearly forming verticils when com- 

 pared to the branches on the other edges. The branches become 

 shorter towards the end of the main spines. The larger branches 

 are in their turn furnished with similar squarrose branches. 



The basal, lateral spines are also strongly developed, although 

 not quite so much so as the sagittal, dorsal one, in other respects 

 corresponding precisely in form and arrangement of branches. 



The apical spine is much less developed, having only a verti- 

 cil of three branches on the corresponding place to the verticil of 

 Plagiacantha, outside this being thin and unbi-anched. 



The ventral, sagittal spine is thin and unbi-anched, almost 

 straight, pointing obliquely dowmvards between the latcial spines 

 and being somewhat shortei- than these. 



In addition, in well developed foi-ms, there appears to be two 

 strong, lateral arched branches extending from the basal, dorsal 

 spine at the base of the apical spine. These arched branches form 

 a pair of secondary, lateral spines, Ij. and Ij, in form and arrange- 

 ment of branches corresponding to the primary, lateral spines, only 

 less developed. In those individuals where a smaller numbers of 

 secondary spines were developed, they -wei-e not visible. But it 

 must be remarked that the species is very brittle, so that the 

 branches are easily broken ott'. 



This species is especially interesting, as it seems to show the 

 evolution of the ring species. Cfr. above and under the follo\\-ing 

 species. 



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

 Seems to be boreal oceanic. 



Disfriljiition: Otherwise only observed on the west coast of 

 Norway: Tiie Oster Fiord, very scarsc. in deep watei-. 



\ II C. 2. Ntephoidea lie k. (Ntcplianida and 

 Seiiiantida). 



Diotyocircns n. !,^en. 

 (Cfr. pi. XIII, f. 48). 



A strong, sagittal ring, one side, the doi'sal, being less bent 

 than the other, the ventral. (This peculiarity of the ring species 

 is also mentioned by Haeckel). This ring is in the following de- 

 scription supposed to be placed downwards, not upwards as by 

 Hakckel. 



