27 



plates are here only seen in the distal half of the zooecium, 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 rule, because, namely, the distal 

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

 belongs really to the distal zooecium. We can easily convince ourselves that the 

 same law applies to the pore-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, fig. 3 c). If we sepa- 

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

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

 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~ zooecium meets the basal 

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

 the lateral walls in the proximal portion of the zooecium, which is provided with 

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

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

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

 thej' 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 zooecium the 

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

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

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

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

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

 plies to the opening of the pore-chamber, which is limited by 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 opposite zooecium the lips here are a part of the real pore-chamber, and 

 the opposite zooecium 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 zooecium, namely, that the distal half of the zooecium 

 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 zooecia as are arranged in regular quincunx, i. e. so that a 



• 54, PI. II, figs. 27—33, 55, PI. IV, figs. 22—32. 



