Protistplanktc 



131 



riir-iis datliratiis, only tliat, on liotli sidrs of llir sauittal rin^"-, 

 tlicro is a further dovclopmeiit ol' tlic net wmk. wliicli lias become 

 two I'oiuplcte domes, one on each side. 



Till' primaiy pores (nearest tiie sa::iltal rini;) are polytzonal, 

 the otliers beinif irregular roundisli and oblons^' and varying consi- 

 derably in size. The scparatinu' walls arc stionj,'-, with here and 

 tliere narrow, protruding points which form obli({uely diverging 

 narrow spines. There is also a rather plentiful number of similar 

 byspines. 



All the spines arc little prominent, to ', i — '/:■ of the diameter 

 of the sagittab ring. 



The species does not appear to be identical to any of Haeckel's. 



\'ery rare and only singly: The \'est Fiord 'j 1899, 0— 

 •200 ni. 



DititiihHtion: In the warm, .salt waters of the Atlantic beyond 

 .Sondmore (S/S Michael Sars, -/■i 1901, between stations 4 and 5, 

 in the surface; cfr. (Jran. L. 70, p. 14D), very sparsely; the 

 Oster Fiord neai- llergen, at a great depth, here too only singly. 



VII C. 4. .llonocyrtida Hck. 



The genera Plechuanthd and PhonnacimtJui. as also the genus 

 Frofoscenium, should properly be referred to the group Plectoidea 

 Hck. (in account of their more or less incomplete skeletons), but 

 is placed here in order not to break their natural connection with 

 the following genera. 



Plertaraiitlia u. geu. 

 (PI. XIII, f. .50— .58). 



Has the foui- primary spines, the sagittal, dorsal, basal one, D, 

 the two ventral, lateral, basal ones L and Lj, as well as the sa- 

 gittal, apical one A. Besides there are, between these, three pri- 

 mary arches developed, one ventral, B^,, between the ventral, la- 

 teral spines, and two lateral V,^. and Bj, between the dorsal, basal 

 spine and the right and left lateral one. In this way, 3 large, 

 pentagonal meshes are formed, the piimary ventral mesh, the pri- 

 mary right lateral and the primary left lateral meshes. 



Ås mentioned above in the general remarks on the N'asselluria 

 group, the ventral mesh and the left, lateral one have as a side 

 in common a short branch which descends from the under side of 

 the left, lateral spine, while, on the other side, the right, lateral 

 mesh and the ventral mesh reach immediately up to the right, la- 

 teral spine. 



There is no ventral, sagittal spine extending from the common 

 .starting point for the two ventral, lateral main spines. 



In addition to these primary spines and arches, secondary ones 

 are also more or less developed, and form a comparatively rich 

 network, which is, however, open, or very imperfectly closed 

 beneath. 



P. oikiskos JiJRO. 11. nomen. 

 (Pl. Xra, figs. 50—57). 



Periplecta intricata (Cl.) JoRfr. L. 91, p. 73. 

 Peridium (?) intricatum Cl. L. 30, pi. 2, f. 8 a, b? 

 Pcridium (?) la.rnyn Cl. 1. c. pi. 2, f. 9 a, b? 



The primary verticil of branches of tiic apical spine has (ge- 

 nerally?) only two branches, pointing upwards and outwards in the 

 angle between the dorsal, basal spine and the lateral ones. These 

 two branches together with the protruding middle stem form three 

 undivided spikes, about e((ual in length. 



The left, latei'al spine, L[, has the primai-y verticil complete. 

 Of these three branches, however, the inside one (l.j in fig. \ , p. 

 124) is — as previously mentioned — transformed into a shoit, 

 strong arch, pointing downwards, at the end of which the left, 

 lateral arch and the primary, ventral one meet. The two other 

 branches form with the protruding middle stem, three, diverging-, 

 long, single spikes, pointing obliquely outwards and to the sides. 

 By these thi'ee long, protruding spikes, the left, lateral spine may 

 always be easily recognized. 



The right, lateral .spine has only retained one branch of the ver- 

 ticil in its original form, the other two being branches for the two 

 corresponding, primary arches, one belonging to the ventral arch, 

 the other to the right, lateral one. There are consequently here 

 two long, simple spikes, about e(iual in length, the outer brancli 

 in the primary verticil and the protruding, middle stem. 



The dorsal, basal spine has only one simple branch of the 

 verticil, pointing outwards and upwards (dj in fig. V, p. 124), the 

 two others being strong, arched branches, diverging- nearly at right 

 angle on both sides. 



One of these branches forms the right, the other the left la- 

 teral arch. The middle stem of the basal spine is here branched, 

 there being one or two similar secondary arches outside the pri- 

 mary, lateral ones. The dorsal, basal spine, therefore, only shows 

 one simple, protruding spike, A similar, smaller byspine is gener- 

 ally to be found farther out. 



The dorsal spine is the longest and strongest, the apical one 

 is shortest and weakest. 



Outside the primary meshes, secondary ones are developed 

 more or less richly, varying considerably in size. These unite to 

 form a „network" which is generally rather imperfect, but would 

 seem, on older individuals, to be made more complete by the ad- 

 dition of connecting beams across the larger, secondary meshes, so 

 that these meshes finally are smaller in size and more in number. 

 Generally speaking, the network is conically expanded downwards, 

 and seems, in the case of older indi^iduals, finally to be imperfectly 

 closed beneath by the development of a few, fine, long, transverse 

 beams. In the material examined specimens with such nearly closed 

 network were always rare. 



(Jf the more important byspines and secondary meshes, 1 \\ill 

 only mention the following which seem always to be present, and 

 may serve to help in identifying the species. Under the protruding 

 right lateral spine a large, secondary, pentagonal mesh will be 

 found. The left, lateral arch has a strong byspine in the middle, 

 pointing outwards and upwards, and under it, there is a large, se- 

 condary mesh. On both sides of the dorsal spine, outside the pri- 

 mary, lateral arches, on the left side will be found two secondary 

 meshes, and on the right side one; the latter being the largest, 

 but it is perhaps later on divided into two. 



iloreover, on all the stronger arches, there is a more or less 

 rich development of byspines, pointing outwards and upwards, some- 

 times twins, directed upwai'ds-outwards and downwards-outwards. 



The beams are thin in young individuals, especially at the 



