(jl 



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

 reous plate, which has arisen IVom calcilication of a part of the frontal mem- 

 brane of the zoo'cium, 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 zooccium and the ooicium, is the basal wall of the oa'cium, 

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

 ou'cial fold, arising in the circumference of the plate named. The inner layer 

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

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

 calcareous framework. 



The calcification of the basal wall of the endoooecium takes ])lace in CaUo- 

 poni Ihimcrili (PI. IX, fig. 3 a), C. aiirita (PI. IX, fig. 4 a, PI. XXIV, fig. 16), 

 Teijella unicornis. T. .Srj/j/ifV/e (PI. IX, figs. 6 a— G c) and Crihrilina punctata (PI. IX, 

 figs. 11a — lid) in the .same way as m Scrap, scabva, and the oo'cium in these is 

 at a very early stage represented by two small sejiarated calcareous plates, l)ul 

 the endoofficium in Caberea Ellisi (PI. II, fig. 6 a) and Demlrotwmia Murraijamt 

 (PI. IV, figs. 2 a — 2e) 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 orecia in the family Onchoporidae, in which the endo- 

 oo'cium as well as the ectoocrciuni is membranous, the endoocrcium seems else- 

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

 extremely thin-walled and breakable, and often not easy to discover on dried 

 material. The ectood'cium may sometimes be membranous, sometimes wholly or 

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

 the family or genus. We have for instance a calcified ectooci'cium in the families 

 lielcporitlae, Sniitlinidac and Di.scoporidae, in the genus Cellepora, besides in most 

 of the Porella species, l)ut we find a membranous one in the genera Scijizoporelld. 

 Hscharella, E.scliaroide.s and Pelralia. In the species of the genus ('.(diopora (PI. XXIV, 

 lig. H)) a larger or smaller portion of the ectoooecium is membranous, and the 

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

 just the proximal border for the calcified i)ortion. The eclooo'cium 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 develojjed crypto- 

 cy^tic region may appear in the endoorecial od'cia, between the two layers of 

 the Od'cium, and the same may be the case in the hyperstomial ones. Still I 

 have up lo now only found such a cryptocyst in the genus luuballotlivca (PI. 



