146 R. M. Brydone — New Chalk Polyzoa. 



at the top of the (restricted) zone of A. quadratics, it is very doubtful 

 if it persists into the zone of B. mucronata. It seems to be succeeded 

 in the base of the latter zone by the following species. 



Membraniporella manonia, sp. nov. (PL IX, Figs. 4-7.) 



Zoarium free or incrusting, multilaminate when free, generally 

 multilaminate but occasionally unilaminate when incrusting. 



Zooecia of medium size but very variable, average length from 

 •55 to '7 mm. : the primary zooscia have semicircular apertures with 

 a denticle on the lower lip and arched front walls arising from just 

 within arched side walls and pierced by four or five pairs of long 

 wide slits: the secondary aperture is formed as in the preceding 

 species, but is rather contracted and keeps much lower, occupying 

 a more or less central position in a gentle eminence, in the sides of 

 which there are generally two but occasionally one or three rather 

 smaller holes of irregular shape ; the encroachment on the front wall 

 by a thin horizontal lamina, which in the preceding species takes 

 place only at the upper end, takes place in this species all round the 

 front wall until in the older parts of the zooecium only a small hole 

 of irregular shape is left, at the bottom of which the front wall can 

 hardly, if at all, be seen ; the side walls coalesce and swell up to the 

 general level, and the zoarium becomes an undulating expanse devoid 

 of features except scattered holes, and resembling the surface of 

 a Calcisponge such as Manon. 



Ocecia. — There are practically no suggestions of ocecia among the 

 peripheral zocecia, and it is therefore improbable that they are 

 represented by any of the holes which form the features of the mature 

 zooecia. 



Avicularia are probably the origin of the holes accessory to the 

 secondary aperture, although no ordinary avicularian structure is 

 preserved in them ; these avicularian holes occur usually in pairs 

 beside the aperture, but one may be suppressed or a third added 

 above the aperture ; they lead to deep chambers. This species occurs 

 very consistently in the lower part of the zone of B. mucronata, to 

 which it seems a very reliable guide, in Hants and the Isle of "Wight : 

 no trace of it has yet been observed in any chalk that could be 

 attributed to the zone of A. quadratics. All the figures represent 

 segments of circular patches selected to show the passage from young 

 to mature zocecia. 



Membraniporella transligata, sp. nov. (PI. IX, Figs. 8, 9.) 



Zoarium unilaminate, incrusting. 



Zooecia small, average length -5 to "6 mm. : the primary zocecium 

 was apparently of the same general type as in the two preceding 

 species, the semicircular aperture having a very thick denticulated 

 lower lip, from the lower side of which a broad process descends to 

 a very short front wall arising rather deep within wide common side 

 walls and pierced by three or four pairs of fairly wide slits and 

 having generally a dwarfed appearance : this aspect passes rapidly, 

 by a forward and upward thickening of the lips of the aperture and 

 a general raising of the side walls and their throwing out lateral 



