270 



ever cover the whole of the aperture. Finally we find in a niiiiiher of species of 

 the genus Hipjjotlioct partly unusually small or unusually narrow zod-cia with 

 aperture and operculum of the ordinary structure, partly dwarf zoa-cia with a 

 dilTerent form of operculum, which does not cover the whole of llic ajx-rture, 

 and last of all kcnozocrcia. hi conclusion I luay just mention that while the 

 separate chamhers of the colony are connected by small pore-chamheis, the 

 septum between the gonozoa'cium and the kenozocecium covering the od'cium is 

 provided with a row (in H. luidliiid with 4 — 6) of uniporous rosette-plates. 



Synopsis of the genera. 



1) The aperture with a simple operculum: 



2) A median ascopore proximally to the aperture; oa'cia covered 



by kenozocecia; zocEcia with scattered pores Haplopoma n. g. 



2) No median ascopore; ooecia covered by avicularia: the zocrcia 



with at most a row of pores on each side Chorizojioni llincks. 



1) The aperture with a compound operculum, which is generally 

 provided with a sinus: 



;{) Oa>cia covered by kenozoa^cia; zoeecia without pores. . . flippolhon I^amour. 



3) Oa^cia covered by dwarf zocecia with ojjcrcula; zoacia with 

 scattered pores Triiposte</a n. g. 



Hippothoa I^amour. 

 Hippothoa Hincks, Schizoj)()rella llincks, Diazeuxia Jull. 



The zoa'cia have no pores, and the aperture is provided with well-developed 

 hinge-teeth and has .generally a sinus, more seldom a convex proximal margin. 

 A compound operculum with a broader or narrower accessory [)art. The gono- 

 zoo'cia bearing the 0(ecia have an operculum with a very small accessory part, 

 and the o(rcia are surrounded by kenozoa-cia without aperture '. 



Of the numerous species belonging to this genus only a smaller numhui- have 

 been described. They differ in form of aperture and hinge teeth, in the absence 

 or presence of acropetal spines, in position and structure of the gonozoo'cia, in 

 structure of the kenozocecia, in mutual connection of the zocecia, etc. The difler- 

 ence in position and structure of the gonozocrcia a])pears from the fact, that 

 these individuals in some species (e. g. in H. corniilit) are situated on a level 

 with the other zooecia and are of similar size and form, while in other species 

 (e. g. H. hijalina and //. (iimiihiris) they are situated on the frontal wall of the 



PI. XVIII, fi". 9 a. 



