23 



oped, more chitiiiised projecting marginal |)ortion, »the pore-rings the onter open- 

 ing of which in the most developed rosette-plates is smaller than the size of 

 the plate a little in from it. Within the pore-ring we can distinguish hetween 

 two portions, differing in thickness, a thicker outer area and an inner surrounded 

 by the other, very much thinner and very small pore-area, which is pierced by 

 an extremely fine pore, and distinguished by a strong bluish lustre, which at 

 lirst glance makes it seem thickened. Such one-pored rosette-plates may appear 

 singly (the distal wall of Flnstru seciirifrons, Fl. papyred etc., the distal wall of 

 most Reteporid(te), in a more or less numerous (of 2 — f2 plates) series (all walls 

 in many species of Sniittina, in Adeonidae, in mosl Fliistridae), or in groups some- 

 times consisting of more scattered, sometimes of more closely placed plates (e. g. 

 in Cotenariidae, the distal wall in Scrupocellaviidue and Thalamoporellidae). hi 

 cases where tiie single rosette-plates are close together, they have a scjuare or 

 hexagonal shape, and meet in a network of elevated ridges, which must be re- 

 garded as the ])ore-rings for the single rosette-plates. 



It is (juite impossible to draw a sharp limit between a group of one-i)ored 

 rosette-plates and a multi])orous roselte-plafe, as the only character, which can 

 be regarded as peculiar for the multiporous compound rosette-plate, namely, a 

 common pore-ring which surrounds all the single small plates, can be developed 

 to very different degrees, and does not always appear to be constant even in the 

 same colony or in the same zooecium. This is the case with for instance Arthro- 

 poma Cecili, in which species the distal wall as well as the distal half of each side 

 wall is furnished with an elongated or oval group of numerous iiniporous rosette- 

 plates. A pore-ring may be lacking on some walls and appear on others, not 

 only in the same colony but also in the same zooecium, and wherever it appears, 

 it may either be exceedingly well developed, or only slightly indicated. Within 

 the pore-ring (PI. XVII, tigs. 10 a, 10 b) which has a similar structure as in the 

 uni[)orous rosette-plate, we have an area, the large area, which may be tilled l)y 

 the small plates to a very different degree, and while these for instance in Artliropomn 

 Cecili often form only a longitudinal belt along the middle part, in ^Lepraliw 

 Pallasiana (PI. XVII. (ig. 10 a) they fill the whole or at any rate the largest part 

 of the plate. The rosette-plates may show many ditTerent degrees of calcification, 

 to some extent according to the degree of calcification of the sjjecies concerned. 

 In most members of the family Bicellnriidae, in species of the genus Onychocellci 

 and Selenaria we thus lind rosette-plates, which with exception of the pore-ring 

 are quite uncalcified; on the other hand we find e. g. in Fliislra foliacea and 

 Flnstia carbacea, that the large area is calcified and the single small plates are 

 uncalcified. The pore area is always uncalcified, while on the contrary the outer 



