1(U 



with a peculiarly formed ai)crlurc, whereas neither the description nor the figures 

 of M. centralis give any indication of the presence of such zooecia in that species. 



Hemiseptella n. g. 



From the proximal margin of the primary aperture a horizontal lamina 

 taking up the whole hreadlh of the frontal wall, descends some way into the 

 zod'cinm. The j)rimary aperture is more or less completely divided into a distal 

 portion, containing an opercular valve with a strongly chitinized opercular arch 

 and a proximal portion, represented by the two oi)esiuhe, the division being 

 efl'ected either by the concrescense of two or three laminate processes or in a 

 very incomplete way by three (two lateral and a median) group of s])inous pro- 

 cesses. Small (iviculdi'ut. No i)ores and no spines. No (xrcia. The lateral walls 

 are common to the contigimus zoo'cia. Large generally uncalcilied rosette-plates 

 with several ('?) j)ores. Free branched colonies with pillar-like branches and strongly 

 calcified zocecia. 



To this genus belong Viiicnl(iri(i gntliica Busk* (= V. ste<i<in(tpiir<ndes Goldsl.), 

 Vine, hibiata Busk and "Thalamoporelhi'^ Michaelseni Ca\\e[", in which last species 

 the division between the opercular aperture and the two opcsiuhe is very in- 

 complete, being only formed by three separate groups of spinous processes. 



To judge from the figures, a number of the species, referred by d'Orbigny-', 

 lo the genera Cellitvui. Quadricelhtria, Vincnlaria and Vincnlarind are no doubt 

 related to this genus, and Vincnlnrid yotliicd"^ is at all events nearly related lo 

 Hem. sleganoporoidcs Goldst. A similar form of aperture is found in Semicscliara 

 himarfiinatd d'Orb.', and in Vincnlarind ohliqna^ d'Orb. the little avicularium has 

 the same position as the avicularium in Hem. steganoporoides. 



Having examined a piece of Heiii. steganoporoides and several pieces of Hem. 

 labiatd, all from the Challenger Expedition I have come to the result, that the 

 two forms are only local varieties, not distinct species, and firstly Hem. stegano- 

 poroides in opposition to the contrary statement of Busk is furnished with a quite 

 similar avicularium as is found in Hem. l(dnat<i. The chief difference however 

 between the two forms is according to Busk to be found in the different origin 

 of the central pier which separates the two opesiuhe, this j)ier being in Hem. 

 steganoporoides formed as an ascending process from the proximal margin of the 

 primary aperture, while in Hem. lahiahi it is formed as a descending process 

 from the bridge, which is itself formed by a concrescense of two lateral pro- 

 cesses. In a number of zoa'cia of Hem. l(dnata I have however found a more or 



8, p. 72—73; 110, p. 13. ■' 11. p. 18. " SB. * 86, PI. 6o4. ■"' 80, I'l. 6(>0 



