68 



further development. The zooecial aperture, then, is horizontal (the zooecion supposed 

 to hold that position), semielliptical, with well defined, a little raised rim, and with 

 the proximal margin slightly concave. Its breadth, then, can be rncasured to be about 

 0,08 ram. ; its length to about 0,06 inm. Above this, the irregularly tubular secondary 

 aperture raises itself, directed obliquely distally, in growing upwards taking with it, at 

 its sides, the continuation of the above-named crest. The distal part of this tube very 

 often fails, the secondary raising, then, ending abrnptly, laterally, at the crest. The 

 proximal part is bent, in its iniddle, in a sinus, thus, in its growing upwards, produc- 

 ing, internally, a rounded furrow, corresponding externally to a rounded median ridge. 

 In connexion with this bending, the lateral avicularium is developed at the one of the 

 longitudinal impressions, or furrows, which externally limit the above-named ridge. In 

 the European Eetepora cellulosa, this avicularium, Avhen not replaced by a great acute 

 one, is very small '), and in producing upwards (towards the zooecial aperture) the 

 margins of its aperture, attains that slit-like appearance, at first pointed ont by Busk; 

 here, in the Ret. marsupiata, it gains a greater development, although, sometimes, it 

 may fail, another time, in the same colony, one may find it rounded and immersed in 

 the secondary zooecial aperture, as well as with an acute mandible, highly pointing 

 outwards obliquely. Beside these avicularia, small rounded ones, with elliptical aper- 

 ture, are irregularly distributed on the front side of the stem. The ooecia are roun- 

 ded, a little elongated, with a longitudinal (vertical) slit in front. While all these or- 

 gans are developing themselves, the zooecial wall, by the advancing calcitication, löses 

 its hyaline condition, grows thicker, and the surface of the stem is rendered inore or 

 less even, by filling up the limitar furrows between the zooecia. The secondary zo- 

 oecial aperture, then, is rounded, with a proximal slit (the secondary median sinus) of 

 an oblique position, as it is thrown to the one side, by the development of the avicu- 

 larium at the other. The retiform stem varies in the shape of its branches; someti- 

 mes, and this seems to be the case in the deeper regions of the sea, they are narrow, 

 rounded, sometimes, f. i. in the colonies taken at the depth of 16 fathoms, they are 

 broader, flattened. . 



This species, if we compare it with the formerly so named Eschara (Escharoides) 

 rosacea 2 ), evidently belongs to the same genus. The primary shape of the zooecia, 

 the primary as well as the secondary zooecial aperture, the oral avicularium as well as 

 the small, rounded ones, scattered on the secondary surface of the stem, are almost all 

 the same. 



The differences refer to the limitar crest of the zooecia, the slit on the ooecia 

 and the development of the great, acute avicularia, in the Retepora marsupiata. The 

 difference in the form of the colonial growth can not be of any generical value. 



') The correspondence between the small, slitlike and the great, acute avicularia, in the typical Ret. cellulosa, 

 is not yet fully demonstrated; but, as they hold the same position as in the Ret. marsupiata, that corres- 

 pondence is at least highly probable. 



'*) Compare I', i. our figure 254 with the flgs. 15G and 157 in the Pl. XXVI in ÖtVers. Vet. Akad. Förh. 

 1867! 



