R. M. Brydone—New Chalk Polyzoa. 99 
avicularia, and its general sleekness of appearance are points which 
effectively distinguish it from the typical and abundant free-growing 
form of the zones of A. quadratus and O. pilula, but are hardly of 
specific value, indicating rather a stage in the development of a single 
persistent form. To emphasize the range of evolution in this species 
J have added a figure of the form of the zone of If. cor-testudinarium, 
which is practically the earliest known. 
MemBRANIPORELLA PontIFERA, nov. (PI. VI, Fig. 8.) 
Zoarium unilaminate, adherent. 
Zoecia slightly pyriporiform; areas oval with flattened upper end, 
average length *35mm., breadth -2mm.; side walls broad and 
bearing about six pairs of stout imperforate tubercles; in three 
instances in the type-specimen the area is bridged between a pair of 
tubercles by a broad arched bar without any lateral connexion or 
even suggestion of it. 
Oecia only known from damaged specimens, apparently of globular 
type; at the point of attachment to the front wall they generally 
absorb part of the highest pair of tubercles. 
Avicularia small, interstitial, mandibular, with a slender transverse 
bar occasionally preserved quite perfect. 
The figured specimen is of course very imperfect, as it must be 
assumed that in a perfect specimen all or nearly all the pairs of 
tubercles would be connected by bars in every zocecium ; but it could 
only be by the merest chance that such a specimen would be secured, 
and no amount of waiting would guarantee it. ‘The species is an 
obvious warning against hasty diagnosis of forms that look like spiny 
Membranipore; but it is probably a safe rule, as the front wall 
elements of Membraniporella were presumably always fixed, that that 
genus is not in question when any of the tubercles are perforate and 
presumably bases of movable spines. 
The species occurs very rarely in the zone of UW. cor-testudinarium 
’ in Hants and the zone of If. cor-anguinum at Gravesend. 
MeEMBRANIPORELLA oBscuraTa, nov. (PI. VI, Figs. 9, 10.) 
Zoarvum adherent, almost always more or less multilaminate. 
Zowcia very small, average length -4 mm., with heel shaped to 
horseshoe-shaped apertures (the outline depending a good deal on the 
amount of encroachment of avicularia), the lower lip of which is a 
straight thickened bar generally bearing a distinct median denticle ; 
the slightly arched front wall should be pierced by four or five pairs 
of radiating slits, as seen in Fig. 10, but it is only rarely that this 
structure can be detected, although the general aspect is so 
emphatically Cribrilinid that I never doubted that it would prove to 
belong to that family. 
Owcia. No trace observed. 
Avicularia small, probably mandibular, scattered in abundance 
along the interzocecial furrows, which they almost wholly obscure and 
often fill up to above the level of the zoccial front walls. 
This species appears to be confined absolutely to the zone of 
M. cor-testudinarium, in which it is fairly common in Sussex and 
occurs also in Hantsand Kent. Its general indistinctness is, of course, 
