13:^ 



E. Jørgens 



outer secondary meshes; they are much stronger on older indivi- 

 duals. 



The length of tiie basal, dorsal spine is + 55 [i.. 



Cfr. JOEOENSEN 1. C. 



I considered this species first to belong to the genus Perq^lecta 

 HcK.; but as I later on found that what with Haeckel charac- 

 terises this genus is also characteristic of all closely related ge- 

 nera, as I am acquainted with them from plankton samples (not 

 di'awings), I have been obliged to change the name of the genus. 



I at first considered this species to be Cleve's PeruJium infri- 

 €atum, and this may be correct, but it cannot be proved to be so 

 from Cleve's illustration nor from his description. As it is, more- 

 over, quite as probable that Cleve's Peridium (?) laxum also belongs 

 to this species, I consider it best to retain the manuscript name I 

 originally had given the species before Cleve's work was pubhshed. 



Not rare, but always in small number. 



Distribution: Not rare on the west coast of Norway, always 

 scarce. Probably boreal oceanic. 



P. trichoides J org. n. sp. 

 (PI. XIII, f. 58). 



Peridiimi (?) huum Cl. L. 30, pi. 2, f. 9 a, b? 



I have only an imperfect knowledge of this species, as I 

 have only seen a few specimens, and at first took these to be- 

 long to the preceding species. 



It has the same primary spines and primary arches ; but there 

 appears to be the important difference that the ventral, primary 

 arch and the left, lateral arch both extend to the left, lateral spine, 

 not to a common basal branch from the latter. On the other hand, 

 there is a strong, secondary arch between the left, latei'al one and 

 the nearest side of the primary, ventral one. 



In outer appearance, this species is very different from the 

 foregoing one. Instead of the numerous secondary meshes, long 

 connecting arches are developed, which form together a longish, 

 ovate, very imperfect network of long, fine arches. The largest 

 and strongest of these run between the two lateral arches and form 

 a vei-y large, ovate mesh, pointing downwards. On its sides, espe- 

 cially in a ventral direction, similar large meshes are developed, 

 bounded by fine arch branches, which run from the primary arches 

 to tlie said large, secondary one, or between secondary arches. On 

 these; arch branches, very fine spines are scattered, these probably 

 latei' on being developed into arch branches between the secondary 

 arches. It is likely that a network wil appear which is imperfectly 

 closed beneath by basal, secondary arches, on elder individuals. 



On the primary, basal spines, short byspines are also found 

 on the pieces inside the primary arches. 



This species is undoubtedly different from the foregoing. It is 

 not certain whether it should be reckoned as belonging to the 

 same genus; but it wants, as does the foregoing one, the ventral, 

 sagittal spine. 



Very rare and scarce, though certainly to some extent over- 

 looked: '7i 1899, 40 miles N. W. of Gaukværo, 0—700 m. 



Distribution: .\lso on the west coast of Norway, but only 

 occasionally and in small numbers. 



I'lioi-iiiiicaiitlia a. gen. 



Has the same four primary spines and the same three primary 

 arches as Plectaecmtha. There is, however, also a ventral, sagittal 



spine, which is less strongly developed than the others („der se- 

 candare Mittelstachel", Jorgensen L. 91, p. 77). The netwoi'k, 

 as in Plectaecmtha, is at a late stage and only imperfectly closed 

 beneath. 



P. bystrix (Jobg.) 

 (PL XIV, figs. 59—63). 



Pmdiiim hystrix Joeg. L. 91. p. 76. 



The primary spines and primary arches as in Pkctacantlta 

 oikislxs. The venti-al arch and the left, lateral one also here run 

 together to a strong, basal arch bi'anch from the left, lateral main 

 spine. 



Outside the ventral, sagittal spine, there is an extended net- 

 work of numerous, secondary meshes, which both below and on 

 the sides are connected by fine transverse beams to a correspond- 

 ing one on the sides of the dorsal sagittal spine. In this way a 

 network is formed, wliich is imperfectly closed beneath. 



There are numerous byspines. Between these and the lar- 

 ger beams more or less numerous and mostly thin, arch-shaped, 

 connecting beams are extended, which are in their turn here and 

 there connected by similar, arched, fine beams, which at a later 

 stage of development are provided Avith numerous, fine spines. 

 These are, possibly, later, at any i-ate to some extent, developed 

 to similar fine connecting arches, which more or less completely 

 envelope the network. 



The development of the arches is here further advanced than 

 in Plectacantha oiJdskos. From the three branches of the apical 

 spine, arch branches extend, the apical arches, one to the dorsal, 

 basal spine, and two to the primary, latei-al arches. These apical 

 arches may at the corners, as well towards the apical spine, as 

 towards the dorsal one and the primary arches, be enveloped by 

 similar arches. 



Cfr. also Joegensen 1. c. p. 77. 



At a younger stage, this species strongly resembles Plectacantha 

 oiMskos. The ventral, sagittal spine, however, makes it easy to 

 distinguish between them. At an older stage, they are so different 

 that they can hardly be confounded. 



It is likely that there is moi-e than one species which belongs 

 here. 



This form is very interesting, clearly being a connecting one 

 between the groups Plectoidea and Monoeyrtida. I formerly' con- 

 sidered it to belong to the genus Peridium, and there is hardly 

 any great or important difference in the structure of the genera 

 Peridiam and Phormacantha. It seems, however, most practicable 

 to separate the imperfectly latticed forms from those which have a 

 regularly developed lattice work which is closed beneath. 



On the other hand, this genus — as more fully explained in 

 the introductory remarks to Nassellaria — forms clearly a transition 

 to the genera Euscenium Hck. and Cladoscenimn Hck. When the 

 apical arches are further developed, an enclosed spine will result, 

 a „columella". 



T'he larger forms have a ,,network'', which is about 70 \>. in 

 height. 



Ivathei' freciuent, though never numerous, in deep water samples. 



Distribution : The same as that of Plectacantha oilcishos. 



<wOiiosi>li»'ra JuRG. n. gen. 



The very peculiar, little species which belongs here, seems to 

 be constructed in the following way: 



