20 
Bugula versicolor appears to be a Frustra. Membranipora flustroi- 
des and M. serrata Mac Gill, both of which possess endozooecial 00e- 
cia and vicarious avicularia, must be regarded as inerusting species 
of Flustra. Most of the species have only rosette-plates with a 
single pore, and in this division the lower half of the ooecium is 
membranous. Of the species possessing rosette-plates with seve- 
ral pores only a single one, namely F/. foliacea is provided with 
o0ecia in which also the lower half is calcified. 
Bicellariidae. From' the Flustridae with which family the 
Bicellariidae agree in the feeble calcification and in many cases in 
the form of the colony, the members of this family are easily di- 
stinguished by the free hypostegial 00ecia, and the non vicarious, 
freely mobile avicularia. The lateral walls are provided with ro- 
rette-plates with several pores and the distal wall is more or less 
ascending and generally angular from side to side. Waters has 
made the interesting observation that an operculum is not deve- 
loped in the species of Bugula in which the orifice is formed in 
a similar manner as in the Ctenostomata. Another resemblance 
with the Ctenostomata are the stolons and stalks not uncommon in 
this family. In Beania? (Flustra) nobilis Hincks, which has 
hitherto been understood as consisting only of a single layer of 
zooecia, I have in some (dried) colonies (which I owe to the libe- 
rality of Miss Jelly) on the supposed back-side, discovered a layer 
of wholiy uncalcified zooecia without operculum (and consequently 
without 00ecia and avicularia), whereas the zooecia of the front 
side of the colony åre provided with a distinet operculum, but also 
with a similar diaphragma (a ,,setose operculum") as that found in 
the Ctenostomata. The back-walls of the calcified zooecia are pro- 
vided with rosette-plates. These A/cyonidium-like zooecia, which I 
have found in colonies both from Africa and Australia, are of the 
same size as the calcified zooecia with which they alternate. There- 
fore I cannot doubt that both forms of zooecia are really members 
of the same colony. The peculiar dimorphism of this species, to- 
gether with the above mentioned points of resemblance between the 
