29 



marginata (PI. XV, fig. 3 c). On the other hand they are lacking for instance in 

 Flustra foliacea and Fl. securifrons. They appear in the same way as the rosette- 

 plates on the vertical walls, a rosette-plate on a zooecium in the one layer corre- 

 sponding with an opening in the opposite layer, but in none of the mentioned 

 species are they found in all zooecia of a colony, though for the rest they ap- 

 pear in very varying numbers. While they thus appear very scattered in Steg. 

 magnilabris, they are found on by far the most zocecia of Microporella flabellaris 

 and Mic. marginata, and in the last species the connection between the zooecia is 

 as a rule a double one, every zooecium possessing a rosette-plate as well as an 

 opening. 



Rosette-plates or pore-chambers may also appear on the basal wall of colonies 

 with one layer. We thus find a number of uncalcified uniporous rosette-plates 

 in Euthyris obtecta (PI. XV, fig. 2 b) and E. chlatrata * where they might be con- 

 sidered as uniting the interior of the zooecium with the space, which is bounded 

 by the covering membrane, while a number of basal uniporous rosette-plates in 

 Hiantopora radicifera (PI. IV, fig. 6 b) serve as origin for the radical fibres which 

 fasten the colony to its support. In the family which I have called Petraliidae, 

 the species of which mostly appear in free colonies with one layer, the free 

 basal wall is either furnished with rosette-plates or with pore-chambers from 

 which radical fibres sometimes issue (e. g. in Petralia tuberosa Busk^ and P- 

 dorsiporosa Busk^). 



We will now consider the appearance of the rosette-plates on the frontal sur- 

 face. Busk ^ has already called attention to the fact that the species which he de- 

 scribes as Carbasea Moseleyi, possesses a number of formations in the distal half 

 of the zooecium, which quite correspond to rosette-plates, and these plates are 

 also found in the distal part of the frontal wall in Onchoporella bombycina 

 (PI. XIII, fig. 9 a, 9 f), Onchopora Sinclairi (PI. XIII, fig. 7 a, 7 b), Calwellia 

 bicornis (PI. XIII, fig. 8 a) and Onch. dentata (PL XIII, fig. 6 b), all of which species 

 I refer to the family Onchoporidae, and to this family ^Carbasea* Moseleyi and 

 Ichthyaria oculata Busk* also probably belong. The rosette-plates in those species 

 examined by me are furnished with a strongly developed pore-ring projecting 

 into the interior of the zooecium and are either round, uniporous or longitudinal, 

 narrow and as if formed by a fusion together of from two to four uniporous 

 plates placed in one row. To judge from figs. 4 a and 4 b the rosette-plates seem 

 also to be uniporous in ^ Carbasea^ Moseleyi, and the 8 — 10 small red spots, which 

 Busk has found on the rosette-plates of the specimen stained with carmine. 



' 19, PI. XVI, fig. 22; ■■' 8, PI. XVII, fig. 7 d, PI. XVIII, fig. 4 b; ' 8, p. 57; * 8, p. 48. 



