27 



plates are here only seen in llie distal lialf of llie zocecium. and the first, out- 

 wardly arched plate, which can be seen proximally to the margin of the distal 

 wall, only apparently forms an exception to the rnle, because, namely, the distal 

 wall ascends oblitpiely from the basal towards the frontal wall, and this plate 

 belongs really to the distal zoo'cium. We can easily convince ourselves that the 

 same law apjjlics to the [)ore-chambers if we examine the basal wall of a colony, 

 which has such, as the lines in which the pore-chambers meet the basal wall 

 shine through on its surface (PI. IX, figs. 11 g, 12 a, PI. XV, lig. ^ c). If we sepa- 

 rate a row of zooecia of a species which has well-developed pore-chambers, we 

 find that a transverse section of the distal and proximal portions of a zocecium 

 has a very varying form, because the basal part of the lateral walls (or outer 

 walls of the pore-chambers) in the distal half of the zocecium meets the basal 

 wall at a pointed angle (PI. XVII, fig. 10 c), while the corresponding poi tion of 

 the lateral walls in the proximal portion of the zoa'cium, which is jirovided with 

 openings to the pore-chambers, forms an obtuse angle with the basal wall. It is 

 evident fiom this that the zorrcia of such a species, seen from the basal wall, 

 are more or less plainly rhombic, even if when seen from the frontal surface 

 they have an oval or rounded shape '. As the outer wall of the pore-chambers, 

 as said before, forms obtuse angles with the frontal surface of the zocecium the 

 distal half of such a zoiccium will be surrounded by a marginal expansion (PI. 

 XVII, ligs. 1 a, 1 c), formed by the pore-chamber. This expansion which in older 

 zooecia is covered by the surrounding neighbouring zooecia may be easily seen 

 in the marginal zowcia of a growing colony. Just as the opening on the rosette- 

 plate is smaller than its extent a little way inside this (fig. 10 ])), the same ap- 

 plies to the opening of the j)ore-chamber, which is limited bj' two, more or 

 less developed plates belonging to the outer wall, which plates we may call »lips«. 

 They thus play a similar part to the projecting marginal portion of the rosette- 

 plate which we have called the pore-ring, but while the latter always belongs 

 to the op|)Osite zocrcium the lips here are a part of the real pore-chamber, and 

 the opposite zoa'cium has only an opening corresponding to the opening between 

 the lips. 



In expressing as above the law with regard to the relation between the ro- 

 sette-plates and the single zocecium, namely, that the distal half of the zocKCium 

 is furnished with rosette-plates and the proximal with corresponding openings, 

 it should be understood that the word half, taken in a more restricted sense, 

 only applies to such zoa'cia as are arranged in regular quincunx, i. e. so that a 



' 54, PI. II, figs. 'J7— 33, 55, PI. IV, fij>s, 22— M. 



