276 



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

 the genus Hippothoa partly unusually small or unusually narrow zooecia with 

 aperture and operculum of the ordinary structure, partly dwarf zooecia with a 

 different form of operculum, which does not cover the whole of the aperture, 

 and last of all kenozooecia. In conclusion I may just mention that while the 

 separate chambers of the colony are connected by small pore-chambers, the 

 septum between the gonozocecium and the kenozocecium covering the ocecium is 

 provided with a row (in H. hyalina 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; ocecia covered 



by kenozooecia; zooecia with scattered pores Haplopoma n. g. 



2) No median ascopore; ooecia covered by avicularia; the zooecia 



with at most a row of pores on each side Chorizopora Hincks. 



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

 provided with a sinus: 



3) Ooecia covered by kenozooecia; zooecia without pores. . . Hippothoa Lamour. 

 3) Ooecia covered by dwarf zooecia with opercula; zooecia with 



scattered pores Trypostega n. g. 



Hippothoa Lamour. 

 Hippothoa Hincks, Schizoporella Hincks, Diazeuxia Jull. 



The zooecia 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 part. The gono- 

 zooecia bearing the ooecia have an operculum with a very small accessory part, 

 and the ocecia are surrounded by kenozooecia without aperture^. 



Of the numerous species belonging to this genus only a smaller number 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 gonozooecia, in 

 structure of the kenozooecia, in mutual connection of the zooecia, etc. The differ- 

 ence in position and structure of the gonozooecia appears from the fact, that 

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

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

 (e. g. H. hyalina and 'H. annularis) they are situated on the frontal wall of the 



' PI. XVIII, fig. 9 a. 



