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o 
zooecia of Diazeuxia hyalina, iii the corresponding zooecia of Di- 
dymia simplex I have found a polypide of mucli smaller dimen¬ 
sions than those found in the other zooecia. 
2) The hyperstomial ooecia. \Yith the exception of the ooecia 
in Thalamoporella which must be referred to another type, we 
uuite under this name all the external, two-layered ooecia, seated 
over the zooecia or between two contiguous zooecia in the same 
longitudinal row. In most cases it is obvious that the inner layer 
(the endoooecium) can be regarded as a continuation of the distal 
wall uhile the outer layer (the ectoooecium) is formed from the 
front wall of the distal zooecium. This however cannot be the 
case with the ooecia of Cellepora and Schisinopora whose zooecia, 
produced by superficial, irregular gemination, are erect and not con- 
nected wich distal zooecia. Here consequently both layers take 
their rise from the terminal part of- the zooecium. An opercular 
apparatus is hitherto found in Bicellariidæ, Memhraniporidae and 
in Microporella (C al ve t^). It is a membranous fold taking its 
rise from the anterior edge of the distal wall and in Memhranipora 
and Microporella continuous with the posterior wall of the tenta- 
cular sheat. In Bugula, where an zooecial operculum is not deve- 
loped, it is continuous with the posterior lip of the zooecial open- 
ing. An atrium is sometimes present. The ooecia belonging to 
this type we can di vide into two groups, namely into ooecia with, 
and ooecia without, a cryptocyst. 
Hyperstomial ooecia without a cryptocyst. To this group be- 
long the ooecia in the families Bicellariidae, Cellulariidae et On~ 
choporidae. In the first family the ooecia can be characterized as 
free, their ectoooecium having only a very little basal part common 
with the front wall of the distal zooecium and otherwise projecting 
freely. While the endoooecium always seems to be calcified it is 
not always the case with the ectoooecium. In Bugula Murrayana 
f. i. the ectoooecium is for the most part membranous and only 
Op. cit. pag. 57, 169, 262. 
