354 



walled, and the weakly arched IVontal wall is provided with small, round ]iores, 

 as a rule densely placed, which may however be wanting on the part round the 

 aperture. Each of them is more or less surrounded by a raised wall, which is 

 always highest and most strongly developed about the proximal half of the pore 

 and sometimes only distinctly developed round this. The aperture, the anter of 

 which is surrounded by a slight, collar-shaped peristome, varies somewhat in 

 form, as its poster may sometimes be considerably narrower than its anter and 

 sometimes almost reach this in breadth. Opposite its proximal fifth to third it 

 is provided on each side with a triangular projection, within which there is a 

 stout conical hinge-tootii, and whilst the anter of the aperture approximates to 

 the two-thirds of the circumference of a circle, its poster is only strongly arched 

 at the sides and almost straight or slightly convex in the middle. The weakl}' 

 cliitinized operculum is provided with a continuous marginal ridge. Each distal 

 wall is provided inside its basal edge with ca. 10 and the distal half of each 

 lateral wall with 5 — 8 uniporous rosette-plates. 



The ooecia, which occupy the whole breadth of the zooecium, are as a rule 

 longer than broad and their somewhat strongly arched frontal wall is provided 

 with numerous, densely placed, larger and smaller, round or oval pores. The 

 raised network surrounding the pores shows a more or less distinct, concentric 

 striation, and along the middle of each ridge especially there is a narrow, raised 

 line, so that each pore comes to lie at the bottom of a 4 — 6 sided, deepened 

 area. The membranous ectoooecium shows a corresponding division into areas, 

 separated from each other by yellowish, presumably cliitinized lines. The basal 

 wall of the ooccium, which arises a little frontally to the basal wall of the zooecium, 

 rises obliquely up towards the frontal wall and is provided with ca. 10 scattered, 

 round pores. The frontal wall of the onccium projects a little beyond the frontal 

 edge of the prolongation of the distal w-all, so that the egg coming from the 

 zocrcial aperture will be easily led over into the ooecium. 



Avicularia appear on a larger or smaller number of zod'cia to the number 

 of one or two, which are usually placed distally to the ajjerlure, more rarely 

 on the sides of this. They are triangular, but of very different length from differ- 

 ent localities, and the longest of them have the mandible drawn out into a long, 

 thin, terminal j)art. In them all the central third of the subo[)ercular area is 

 covered by a dark, cliitinized, longitudinal belt, which is presumably a part of 

 the covering membrane. These avicularia are fairly short on colonies from St. 

 Thomas (from Pndodesiniis falcatiis) and the mandible is directed ol)li(|uelj' dis- 

 tally and inwards. They are long and narrow on colonies from Singapore and 



