131 



wall has one multiporous plate. Besides dependent avicularia, found in most 

 species, vibracula may also occur on the basal surface of the colony, and these 

 are connected with the colony by an independent wall. The ooecia are generally 

 hyperstomial with a wholly or partly calcified ectoooeciura, more seldom endo- 

 zooecial. In the latter case they are sometimes enclosed in kenozooecia. As a rule 

 radical fibres occur, sometimes springing from a rosette-plate (or a pore-chamber), 

 sometimes from a separate chamber connected with a vibraculum. The colonies 

 are always free, very branched, most frequently with uni- or few-seried zooecia, 

 generally consisting of a single layer and in most cases jointed by means of 

 chitinized transverse belts. 



While a smaller number of species (e. g. Hoplitella armata, Menipea flabellum, 

 Men. spicata ' and the Canda species), have a membranous frontal area, occupying the 

 whole or almost the whole of the frontal surface, a larger or smaller part of the 

 latter is in the other species occupied by an arched gymnocyst which in some 

 species (e. g. in Menipea aculeata Busk and Men clausa Busk) may be up to two- 

 thirds of the length of the zooecium. While the cryptocyst in many species (e. g. 

 in the Scrupocellaria species, in Caberea Ellisi, Menipea aculeata, M. cirrata, M. 

 patagonica) forms only a small depression in the margin of the aperture, it may 

 in other species fill a larger part of the aperture inside the membranous frontal 

 area in the form of a somewhat depressed, generally finely granular lamina. This 

 cryptocyst attains its largest extent in Menipea spicata, Caberea Darwini and in 

 the Canda species, but also in Men. flabellum. Men. roborata (figs. 7 b, 7 c), M. 

 crystallina, M. Baski and several other Menipea species it may attain a consider- 

 able development. We have already mentioned that a number of species possess 

 a wholly chitinized, simple operculum. As in Dimorphozoum nobile and Dendro- 

 beania Murrayana the distal wall consists of a basal, horizontal or slightly obli- 

 que and a frontal, strongly ascending part (PI. II, figs. 7 g, 7 h, 8 c), but while 

 in these two species the former portion is furnished with a single, large, multi- 

 porous rosette-plate, it has generally in this family a great number of single- 

 pored plates which are variously grouped. On examining a zooecium from the 

 frontal surface (PI. II, fig. 7 a), the horizontal pore-bearing part of the distal wall 

 is seen at a deep level at some distance proximally to the distal end of the zoce- 

 cium, and this is seen most clearly after a previous boiling in caustic potash. 

 The avicularia always have their inner wall in common with the zooecium on 

 which they are placed; but as I have succeeded in isolating the vibracula in 

 some species (Caberea Ellisi, Canda arachnoidea, Caberiella benemunita, Scrupo- 



' 69, p. 132. 



9* 



