280 



Haplopoma n. g. 

 The zooecia with scattered pores, a simple operculum and a median ascopore 

 as an orifice for the compensation-sac. The ooecia covered by kenozooecia with 

 scattered pores. No avicularia. 



H. impressum Audouin. 

 Microporella impressa Hincks, British Marine Polyzoa, pag. 214, 



PI. XXVI, figs. 9—11, PI. XXIX, figs. 10, 11. 

 (PI. XXII, fig. 9 a-9 b, 10 a-10 e, PI. XVIII, fig. ll a). 



While Hincks and all later systematic authors have referred this species to 

 the genus Microporella, with the species of which it agrees in the possession of a 

 median ascopore, a simple operculum and pore-chambers, Barrels^ in his great 

 work on the larvae has rightly recognised its relationship to Hippothoa hyalina 

 and called attention especially to the great similarity of their larvae, which be- 

 long to rather a peculiar type. He is however wrong in referring both these 

 species to the same genus (Mollid). 



The supposition, expressed on several former occasions, that the median asco- 

 pore has arisen by a constriction from an original sinus is also confirmed in this 

 species, and Waters^ has already called attention to the fact, that the primary 

 zooecium in H. impressum (PI. XXII, figs. 9 a — 9 b) as well as in H. bimucronatiim, 

 Moll (PI. XXII, figs. 10 a — 10 c) is provided with a sinus, which is however both 

 narrower and deeper in the latter than in the former. The primary zooecium in 

 the latter species is moreover distinguished not only by possessing a curve of 9 

 pores, but also by having an operculum (fig. 10 e) similar to that found in the 

 genus Arthropoma, the accessory part of the operculum, corresponding to the 

 sinus, being separated from the principal part by a less strongly chitinized por- 

 tion. This difference in the primary zooecia also speaks in favour of the opinion 

 maintained by Waters, that H. bimucronatam, which was formerly considered but 

 a variety of H. impressum, is a distinct species. 



Genus Trypostega n. g. 



The zooecia with scattered pores and a compound operculum. The ocecia 

 covered by dwarf zooecia with scattered pores. No avicularia. 



1 1, p. 171, PI. 9, figs. 1—3, PI. 16, fig. 2. " 115, p. 44. 



