482 R. M. Brydone—Chalk Polyzoa. 
only begin to radiate quite close to the foot of the zoarium, and are so 
fine as to be rarely well visible; aperture semi-oval, with a tiny 
denticle in the middle of the lower lip and a thick raised upper lip 
often bearing three or four perforated tubercles; the corners of the 
aperture are overhung by two stout perforated spine bases projecting 
from the upper hp, which often fill up and unite to form an arch 
across the lower part of the aperture; small perforated tubercles 
are scattered irregularly and sparingly on the side walls; these features 
are often very feebly marked. 
Oacia not observed. 
Avicularia may be represented by the perforated tubercles. 
Very rare in the zone of IZ. cor-anguinum at Gravesend. 
It will be observed that the two foregoing species represent a very 
early stage in the evolution of the Steginoporide ; it is curious that 
no species of this family is yet known to occur at any later horizon 
in the English Chalk. : 
MeEMBRANIPORELLA FALLAX, nov. Pl. XXXVI, Figs. 6-8. 
Zoarium unilaminate, adherent. 
Zoecia oval, average length -7--8 mm., breadth *35—-4mm.; the 
arched front wall rests on the side walls, and is pierced by seven or 
eight paired diverging slits extending from the edge’ about half-way 
toward the middle line: aperture semicircular, showing in ordinary 
specimens (Fig. 6) two imperforate tubercles on either side when 
there is no ocecium, the upper pair of which are picked up by and 
form the starting-point of the ocecium when one is formed, as is 
usually the case; the lower lip of the aperture often bears a median 
denticle of very variable size. Such specimens give a delusive 
appearance of organization similar to that of Cribrilina furcifera, but 
in the upper right-hand corner of Fig. 7 there may be observed 
a zocecium which shows that what appear to be a pair (the lower pair) 
of tubercles and a median denticle are in fact the scanty remains of 
the true lower lip of the aperture, which has almost invariably been 
broken away: in another zocecium in the same figure it is preserved 
on one side only. i 
Owcia long and narrow, very generally present; they often appear 
to throw out a sort of causeway leading on to the front wall of the 
zocecium (if any) immediately succeeding the same line. 
Avicularia beak-shaped, small, but very deep, with a slender bar, 
which is rarely preserved, across the aperture; generally lying more 
or less on their sides and with a strong tendency to occur singly or in 
pairs with their beaks directed downwards or inwards at the head 
of the zocecium. Fig. 8 shows a specimen of exceptional regularity 
in this respect. 
The species is not uncommon in the zone of Jf. cor-anguinum at 
Gravesend, and a dwarfed form has been found at the top of the 
zone of Marsupites at two places in Hants. It comes nearest to the 
form figured by Novak! as Lepralia pediculus, Rss., but is easily 
' Novak, Denkschr. d. k.k. Ak. d. Wiss. zu Wien, Math.-Naturw. Cl., 
Bd. xxxvii, p. 98, pl. i, fig. 12. 
