260 R. I. Brydone—New Chalk Polyzoa, ete. 
difference between Pseudostega and Membranipora coralliformis is little 
more than one of degree. 
PsgupostrGa Canriana, nov. Pl. XXI, Figs. 6 and 7. 
Zoarium adherent. “sas 
Zoecia in the lower layer fairly large; length of area *3 mm., 
breadth *2 to -22mm.; in the upper layer they have only vaguely 
defined outlines and are very variable in minute details, but are very 
uniform in general structure ; they run in very straight and regular 
alternating rows, in which, after the initial zocecium, all have a large 
area, with a stout denticle projecting into it at the foot and directed 
slightly downwards, and, as a rule, a small curved indentation opposite 
to it at the head, possibly representing the aperture of an immersed 
ocecium; across the area stretches a broad bar, shaped like a very 
shallow V pointing downwards, which divides the area into two 
compartments, of which the lower is the smaller and is reduced by 
the point of the V and the marginal denticle to the shape of an eight 
lying on its side; at the foot the area is overlooked by two tubular 
prominences on the marginal wall separating it from the area of the 
preceding zocecium; these might naturally be taken to represent two 
avicularia of the preceding zocecium uniformly present in the lower 
layer, but I cannot find any traces of paired avicularia being regularly 
present there, the nearest approach lying in the tiny paired slits 
which can be seen at the head of some of the zocecia of the lower 
layer in Fig. 7, a figure of the only specimen in which the lower layer 
is exposed except at the very edge of the zoarium. The initial 
zocecilum of a row has the point of the V directed upwards and 
a denticle projecting from one side of the upper compartment; the 
lower compartment is much‘reduced and irregular in shape, and there 
is a single tubular prominence at the foot. This general system is 
much obscured by crowding in the early stages of the zoarium, but is 
remarkably regular in the later stages. 
Rare in the I. cor-anguinum zone at Gravesend and Chislehurst. 
Reptescharipora rustica, D’Orbigny, by its general appearance should 
be closely related to this species, but as Canu! makes it a Steginopora 
it must be assumed to have a Cribriline lower layer. 
EXPLANATION OF PLATE XXI. 
(All figures x 123 diam.) 
1. Membranipora Woodwardi, zone of Act. quadratus, Hants. 
», 2. Ditto, zone of Act. guadratus, Hants. Lighted to show up the interior of 
the zocecia. 
3. Ditto, zone of IW. cor-anguinum, Gravesend. 
», 4. M. coralliformis, zone of I. cor-anguinwm, Gravesend. 
5. Ditto, zone of M. cor-anguinum, Gravesend. From the tip of a large 
branching zoarium. 
», 6. Pseudostega Cantiana, zone of W. cor-anguinum, Gravesend. 
5, 7. Ditto, zone of M. cor-anguinum, Gravesend. Lower layer in focus, upper 
layer rather out of focus. 
1 Bull. Soc. Géol. France, 1900, p. 456. 
(Zo be continued.) 
