16 
are seated outside the upper part of the lower zooecium and com- 
pletelj hide the orifice. 
4) The peristomial ooecia. As indicated by the name, tliese 
ooecia are formed by a dilatation of the peristomium, and conse- 
qvently they consist only of a single layer. Such an ooecium can 
be formed either by a pyriform enlargeraent of the whole peristo- 
ihium {Tubucellaria opuntioides, T. hirsuta. ^^Porina'‘'‘ magnirostris), 
or only the inferior part of the peristomium is provided with a 
hemisperical enlargement of its front wall, whereas the rest of it 
continnes its way as a simple tube {hekyihophora hystrix, Turriti- 
gera stellatd). 
5) The mesotoichal ooecia, which are only found in Calymmo- 
phora lucida, are internal one-layered calcified ooecia which take 
their rise from the distal wall and are seated between the cryp- 
tocyst of the distal zooecium and the covering membrane. 
6) The endotoichal ooecia'^). These ooecia, which are only 
found in the family Cellariidae, are cavities hollowed out in the thick 
front wall of the zooecium, and it looks as if they were formed by 
a gradual resorption of the calcareous substance of this wall. By 
a grinding of elder and younger parts of a colony these ooecia can 
be found in all degrees of size, from very little cavities seated in 
the middle of the wall increasing till they occupy most of the 
thickness of the wall. Finally they open outwards. The operculum 
of such an ooecium is as that of the zooecium two-layered, and the 
inner chitinous layer must be looked upon as a non calcified part 
of the cryptocyst. 
7) The bivalvular ooecia, which are only met with in Cate- 
7iaria parasitica, are somewhat compressed, acorn-formed bodies 
consisting of two two-layered arched valves, each of which has its 
place a little outside the orifice of the zooecium. They are seated 
on zooecia whose anterior half forms a right angle with the postc- 
rior half and the basal part of the oeecium covers the whole ante- 
G. M. K. Levinsen, Op. cit. Tab. Il, Fig. 19. 
