Rh. M. Brydone—New Chalk Polyzoa, ete. 259 
elliptical, length -5 to °75 mm., breadth -31 to *45 mm., tapering 
towards the head, across which stretches a slight internal shelf, which 
straightens the apparent outline; from the edge of this shelf hangs 
a stout oval ring, which connects it with the floor of the zocecium ; 
zocecial boundaries distinct. 
Oewcia very large, almost square; the free edge runs out over the 
area for a short distance and is then cut back in a curve parallel to 
the edge of the area beneath. 
Avicularia subvicarious, forming the initial zocecia of new rows; 
they are practically small and narrow zocecia pinched together at the 
top into a beak and spanned slightly below the middle of the area by 
a very slender bar, of which only the broken ends are usually 
preserved ; in the immature stage found in the JL. cor-anguinum zone 
this beak is very short and markedly unsymmetrical, in the higher 
zones it is greatly produced and nearly or quite symmetrical. 
Found occasionally in the zones of IL. cor-anguinum and Marsupites, 
and freely in the zone of Act. quadratus in Hants and in the zone of 
I. cor-anguinum at Gravesend. 
MEMBRANIPORA CORALLIFoRMIS, nov. Pl. XXI, Figs. 4 and 5. 
Zoarium adherent, sometimes tuft-shaped, but very generally forming 
long narrow bands. 
Zowcia elliptical, very small; length of area -24 to :'3mm., breadth 
"15 to °2mm.; primarily they are quite simple, but along the walls 
of mature zocecia there forms a thick, continuous, smooth incrustation 
pierced by numerous short tubes, giving it a madreporiform appearance; 
the tubes show a weak tendency to regularity of occurrence, there 
being usually a pair, one on either side of the upper part of the area; 
this incrustation may overhang the area or recede from its edge, 
which can then sometimes be seen to be studded with tiny perforate 
tubercles; the incrustation often envelops the ocecium, leaving only 
the aperture distinguishable. Among the tubes may be sometimes 
found miniature avicularia. 
Oewcra globose, free edge curved inwards. 
Avicularia vicarious, rare except along the edge of zoaria, wide at 
the head, and tapering towards the foot, close to which they are 
spanned by a slender bar, of which, as a rule, the broken ends alone 
are preserved as a slight constriction of the outline; the broad 
elliptical aperture is coterminous with the walls in the lower part, 
but in the upper part is surrounded by an internal shelf. 
Found in the zone of J. cor-anguinum at Gravesend (abundantly) 
and in Hants. 
PsEUDOSTEGA, gen. noy. 
Diagnosis—A genus of Membraniporide in which a secondary 
zocecial layer is formed over and arising out of a layer of ordinary 
Membraniporidan zocecia. 
This genus seems to be analogous among the Membraniporide to 
Steginopora among the Cribrilinide. The secondary layer apparently 
arises from the walls of the primary layer, and if so the essential 
