61 



the distal wall and soon join in a median suture. This small, bilabiate calca- 

 reous plate, which has arisen from calcification of a part of the frontal mem- 

 brane of the zooecium, increases gradually in size, grows semicircular, and is 

 finally grown round by a calcareous framework of the same origin. The just 

 mentioned calcareous plate with a longitudinal suture in the centre, which forms 

 a common wall for the zooecium and the ooecium, is the basal wall of the ooecium, 

 the frontal part of which is formed by the further development of a fold, the 

 ooecial fold, arising in the circumference of the plate named. The inner layer 

 of this fold (the frontal part of the endoooecium) is a continuation of the plate, 

 while the outer layer (the ectoooecium) is a continuation of the surrounding 

 calcareous framework. 



The calcification of the basal wall of the endoooecium takes place in Callo- 

 pora Dumedli (PI. IX, fig. 3 a), C. aiirita (PI. IX, fig. 4 a, PI. XXIV, fig. 16). 

 Tegella unicornis, T. Sophiae (PI. IX, figs. 6 a — 6 c) and Cribrilina punctata (PI. IX, 

 figs. 11 a — 11 d) in the same way as in Scrup. scabra, and the ooecium in these is 

 at a very early stage represented by two small separated calcareous plates, but 

 the endoooecium in Caberea EUisi (PI. II, fig. 6 a) and Dendrobeania ' Murrayana 

 (PI. IV, figs. 2 a — 2 e) on the other hand calcifies as a continuous plate, and 

 this seems also to be the rule within the division Ascophora. 



With exception of the ooecia in the family Onchoporidae, in which the endo- 

 ooecium as well as the ectoooecium is membranous, the endoooecium seems else- 

 where to be calcified, but in forms with a calcified ectoooecium it is very often 

 extremely thin-walled and breakable, and often rot easy to discover on dried 

 material. The ectoooecium may sometimes be membranous, sometimes wholly or 

 partly calcified, and in many cases its structure appears to be constant within 

 the family or genus. We have for instance a calcified ectoooecium in the families 

 Reteporidae, Smittinidae and Discoporidae, in the genus Cellepora, besides in most 

 of the Porella species, but we find a membranous one in the genera Schizoporella, 

 Escharella, Escharoides and Petralia. In the species of the genus Callopora (PI. XXIV, 

 fig. 16) a larger or smaller portion of the ectoooecium is membranous, and the 

 rib, which Hincks mentions for a number of the species of this genus, marks 

 just the proximal border for the calcified portion. The ectoooecium is also in 

 numerous members of the family Scrupocellariidae provided with a larger or smaller 

 uncalcified portion (PI. II, figs. 7 a — 8 a). 



We have already mentioned previously, that a more or less developed crypto- 

 cystic region may appear in the endoocecial ooecia, between the two layers of 

 the ooecium, and the same may be the case in the hyperstomial ones. Still I 

 have up to now only found such a cryptocyst in the genus Emballotheca (PI. 



