27 
Euthyris obtecta as pointed out by Harmer") this task is performed 
by a number of calcareous processes, and in Calymmophora lucida by 
a keel running down the side-walls of the zooecia. In both species 
the distal wall and the wall between the neighbouring zooecia are 
perforated by a large number of single-pored rosette-plates. 
The renewal of the zooecia. Besides the well known renewal 
of the polypide a renewal also of the whole bryozoid has been 
found im a number of Bryozoa, namely in the Ctenostomatous ge- 
nera Valkeria, Bowerbankia and Triticella in which the old zooecia 
are deciduous and can be replaced by new zooecia taking the place 
of their predecessors. But also in the Chei/ostomata such a rene- 
wal can take place and the presence of a double margin in the 
zooecium of a Membranipora is a proof that a new zooecium has 
here been developed inside an elder one. This form of renewal 
can be compared with that found in the thecaphorous Hydroids ?) 
in which a new hydrothek is formed inside an elder one, whereas 
in the athecate forms the ,,heads" of the hydranths are deci- 
duous and replaced by new ones in the same manner as the 
Z00ecia in the above ctenostomatous genera. Besides in a few 
recent species I have found double (or sometimes triple) mar- 
gins in numerous cretaceous species of Membranipora and such 
double-margitted zooecia have been figured by several authors, for 
instance by d'Orbigny?). In regard to this renewal we can 
discern four different cases, found in the species examined: 1) a 
new zooecium can be developed in an old one, 2) an avicularium 
can be developed in an old zooecium, 3) a new avicularium can 
be developed in an old one and 4) a zooecium can be developed 
in an old avicularium. Besides in Membranipora I have found such 
a renewal in some Cribrilinidae and in Porina flabellata d'Orb. 
nn 
1) Op. eit. 
?) G. M. R. Levinsen, Om Fornyelsen af Ernæringsindividerne hos Hy- 
droiderne, Vidensk. Meddel. fra naturh. Forening, 1892, pag. 14. 
3) Paléontologie francaise, Terr. cret. Bryozoaires, Pl. 699, fig. 2. 
