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ridges, which may sometimes meet in the dislal and proximal pari of Iho area. 

 The operculum, which has usually a jji-oximaj, concave, more seldom straight 

 margin, consists of an outer memhranous pari, continuous with the covering- 

 membrane, and an inner chitinized part, which is connected with the cryptocyst 

 and must be regarded as an uncalcilied part of the latter. This internal layer, 

 Avhich may have a variable sculpture and to the free margin of which the oper- 

 cular arch is attached, shows in the species with the short, rounded supporting- 

 teeth a light, rounded spot on the inner surface towards each corner, which is 

 the mark left by one of the teetli. Wliile the operculum is thus connected proxi- 

 mally with the cryptocyst and covering-membrane of the frontal wall, it has 

 moreover a peculiar, suspensory a|)paratus on each side. On either side of 11 

 namely the inner surface of the covering-membrane is furnished with a curved, 

 linear, cliitinous thickening, a short lateral branch of which reaches as far as to 

 the con-esponding corner of the operculum, joining the chitinous layer of the 

 latter. The two distally as well as proximally convergent chitinous thickenings 

 are separated in most species, but in Cell, magnified they meet distally as well 

 as proximally, while in Cell, allanlica they meet only proximally. Lastly by a 

 sj'slem of filiform chitinous thickenings the covering-membrane is divided into 

 a number of areas corresponding to those of the cryptocyst, and Ihese lliieken- 

 ings are situated in the separating furrows between the separate areas, l)eing here 

 firmly connected with the cryptocyst below. Husk wrongly supposes this fila- 

 mentary net to be hollow. 



The ooecia are as in the preceding family hollow spaces hidden within the 

 surface of the zooecia and opening outwards distally to the zoircial a|)erlure at 

 the distal end of an area but in the proximal end of the zoa-cium. Their frontal 

 wall is sometimes a little projecting sometimes a little depressed, and the outer 

 opening may also be of a varying form, hi most cases it is however (ransver.sely 

 oval with a low but broad, rounded or quadrangularly rounded j)rocess in the 

 proximal margin (PI. VII, fig. 5 a, PI. VIII, figs. 2 a, 1 a). In Cell, /istiilosa the 

 openings are however round at the distal end of a joint. The opening has a 

 bilaminar operculum, which may be drawn into Ihe ocecium by means of muscles. 

 These peculiar ooecia seem to arise by a resorption of the thick fronlal wall of 

 the zooecia, and they begin with the formation of an extremely small cavity 

 (PI. VII, fig. 4 f, PI. VIII, figs. 1 c, 2 b), gradually increasing in extent and ulti- 

 mately opening outwards through the above-mentioned opening (PI. VII, fig. 4 a, 

 PI. VIII, fig. 1 b), which is also formed gradually, Hie initial stage of it being a 

 sma41 slit or pore. By means of a number of longitudinal grindings we maj' find 

 these ooecial spaces in dilTerent degrees of development and when they have at- 



