164 



with a peculiarly formed aperture, whereas neither the description nor the figures 

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



Hemiseptella n. g. 



From the proximal margin of the primary aperture a horizontal lamina 

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

 zooecium. The primary 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 opesiulse, the division being 

 effected 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 spinous pro- 

 cesses. Small avicularia. No pores and no spines. No ooecia. The lateral walls 

 are common to the contiguous zooecia. Large generally uncalcified rosette-plates 

 with several (?) pores. Free branched colonies with pillar-like branches and strongly 

 calcified zooecia. 



To this genus belong Vincalaria gothica Busk' (= V. steganoporoides Goldst.), 

 Vine, labiata Busk and ^ ThalamoporelIa<i. Michaelseni Calvet^, in which last species 

 the division between the opercular aperture and the two opesiulse 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^ 

 to the genera Cellaria, Quadricellaria, Vincalaria and Vincularina are no doubt 

 related to this genus, and Vincalaria gothica^ is at all events nearly related to 

 Hem. steganoporoides Goldst. A similar form of apertui-e is found in Semieschara 

 bimarginata d'Orb.*, and in Vincularina obliqva^ d'Orb. the little avicularium has 

 the same position as the avicularium in Hem. steganoporoides. 



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

 labiata, 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. labiata. The chief difference however 

 between the two forms is according to Busk to be found in the difl^erent origin 

 of the central pier which separates the two opesiulse, this pier being in Hem. 

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

 primary aperture, while in Hem. labiata 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 zooecia of Hem. labiata I have however found a more or 



» 8, p. 72—73; 110, p. 13. « 11, p. 18. ' 86. * 86, PI. 654. * 86, PI. 660. 



