76 R. M. Brydone—New Chalk Polysoa, ete. 
eastern wadies draining into it were formed contemporaneously, also 
by erosion. 
(4) The faulting, which can be observed along the faces of the 
bounding scarps of the Nile Valley, Gulf of Suez, and the eastern 
wadies, is the result of landslips subsequent to the erosion of the 
hollows. 
V.—Nores oN NEW OB IMPHBRFECrLY KNowN CHALK Poryzoa. 
By R. M. Bryponz, F.G.S. 
(PLATE VIII.) 
(Continued from the January Number.) 
Memeranipora Inviertata, nov. Pl. VIII, Figs. 1 and 2. 
Zoarvum adherent. 
Zoewcia roughly elliptical, length ‘60 to -68mm., width ‘86 to°40mm., 
length of area °36 to -40 mm., width -24 to -28 mm.; they have broad 
side walls, whose upper surfaces slope slightly to the area; at the 
foot there is generally a fair amount of external front wall, which 
often carries its own accessory avicularium or the ocecium of the 
preceding zocecium; the walls of adjacent zocecia are always 
distinguishable and very often not in contact. 
Owcia abundant but very. rarely preserved, globose, with a small 
part of the under edge free. 
Avicularia of two types. (@) Accessory: these are small semi- 
circular tubular prominences developed on a semi-elliptical platform 
pushed out over the external front wall below the level of the rims of 
the area; they are directed forwards, looking over the area and some- 
times overhanging it; sometimes the platform is formed without any 
further development, except perhaps a perforation. (6) Vicarious: 
these are long and narrow, widest at the head and tapering gently to 
the foot; aperture similar in outline, but with a construction of very 
variable degree near the foot, and bounded at the head by a broad 
internal shelf at some depth, which tapers rapidly towards the middle, 
where it disappears; at this point the bounding walls are folded over 
so that the outer edge in the upper part becomes the inner edge in the 
lower (well shown by the avicularium, which in Fig. 1 is immediately 
to the left of the only ocecium preserved). 
Fairly common at Trimingham and in the zone of Jheraster cor- 
anguinum at Gravesend, and I have found what may be a spinose 
stage of it in the zone of Actinocamax quadratus. ML. trigonopora, 
Marss., has a general resemblance to this species, but has no vicarious 
avicularia, while this species has not the tiny pores of I. trigonopora. 
Memeranipora Brrrawnica, mihi. Pl. VIII, Figs. 3 and 4. 
I take this opportunity of giving photographs of the type-specimen 
(Fig. 3), and another with finely developed avicularia (Fig. 4). In 
a Membranipora so abundant almost any micrometric measure can be 
obtained, but ‘36 to ‘48 mm. for length of area and ‘28 to ‘32 mm. for 
