lostega and in Camarostega is separated from the covering mem- 
brane by a space containing both leucocytes and mesenchymal tis- 
sue and therefore to be regarded as a part of the original cavity 
of the zooecium. 
While the calcified part of the frontal wall in most Chzei/o- 
stomata is developed under the covering membran and therefore to 
be described as a cryptocyst, a name originally proposed by Jul- 
lien, I have not been able to find a membrane covering the cal- 
careous skeleton of the front wall in the families Onchoporidae, 
Catenicellidae and Electridae, and here this skeleton, for which pro- 
visionally we will use the name a calcified ectocyst, seems to pro- 
ceed directly from a calcification of the covering membrane. Also in 
those members of the families Bicellariidae and Cellulariidae in which 
there is found a calcified postareal part of the front wall, most 
part of this extension is a calcified ectocyst and only the foremost 
concave part of it is seated under the covering membrane of the 
area and consequently to be named a cryptocyst. As already 
pointed out by Harmer the whole of the calcareous skeleton in 
Euthyris obtecta is a cryptocyst and the same is the case in Ca- 
- lymmophora lucida. 
The operculum. While the operculum in most MMalacostega is a 
simple membranous valve, within its margin provided with a chitinous 
bow for the attachment of the opercular muscles, we meet in some 
species of the genus Chaperia (Ch. spinosa and Ch. capensis) with 
a form of operculum for which we will propose the name a compose 
operculum because the opercular valve and the membrane filling up 
the remaåinder of the zooecial aperture are fused together into a 
chitinous plate, both in its darker colour and in its greater firm- 
ness differing from the membrane covering the calcified part of the 
front wall. Only the foremost part (the valvular part) of this 
»Operculum" opens under the protrusion of the polypide. In the 
other Chaperia-species ;we can hardly speak about a compose oper- 
culum, because the correspøndent part is scarcely stronger chiti- 
nized than the membrane covering the calcified part of the front 
