146 R. M. Brydone—New Chalk Polysoa, ete. 
Found in the If. cor-anguinum zone at Gravesend, in the Act. guadratus 
zone in various parts of Hampshire, and in the Belemnitella mucronata 
zone in the Isle of Wight. 
MEMBRANIPORA DoLIum, noy. Pl. XIV, Figs. 4-6, 
Zoarium free or encrusting, always unilaminate. 
Zowcia large; length of area ‘35 to ‘51 mm., with ‘45 mm. as a fair 
meat ; breadth -28 to: 43 mm., with °36 mm. as a fair mean ; the giant 
form from the Cromer-Weybourne Chalk shown in Fig. 6 gives average 
length of area 65 to ‘7mm. and breadth ‘5 to ‘°55mm.; the broad 
margins are quite distinct ; the areas are more or less barrel-shaped, 
owing to the strong tendency at the head to a straight margin, and at 
the foot to a slight intrusion of the preceding ocecium. 
Oecia abundant, large, and globose. 
Avicularia of two types. (a) Accessory: a pair of rings very 
uniformly present set against the areal margin at the upper corners. 
(6) Vicarious: elliptical cells with a wide elliptical aperture surrounded 
by.a narrow front wall; at about one-third of the way down the cell 
the bounding walls are bent inwards until they slightly overhang the 
aperture ; they continue for another one-third of the cell to overhang 
the aperture in a slowly increasing degree, and are then cut back to 
the edge of the aperture at a right angle, and for the rest of the isueth 
of the cell coincide with the margin of the aperture. 
Found in the Act. guadratus zone at various points in Hanpehitee, 
and with B. mucronata at Bramford in Suffolk, and in the Cromer— 
Weybourne Chalk, but not yet at Trimingham. It agrees very closely 
with I. lyra, as fieured by Hagenow,' except that the latter has not 
vicarious avicularia according to cither figure or description, and it is 
not likely that Hagenow would have overlooked them if they did occur. 
MEMBRANIPORA ANGUIFORMIS, noy. Pl. XIV, Figs. 7 and 8: ~ : 
Zoarium unilaminate, always encrusting. 
Zoecia small, length ae area °27 to °32 mm., breadth ‘238 to °26 mm. A 
subcireular, with very distinct margins, and often separated by deep 
fissures. 
Owcia very abundant, but very fragile; the specimens shown by 
Fig. 7 are the only ones 1 have seen, and unfortunately three out of 
the four have become defective and the fourth cracked since that 
photograph was taken; they are very wide, but too short to reach the 
area, with straight free edges, their general shape being much that of 
a beehive; the traces they eave when broken away are very indistinct. 
Avicularia of two types. (a) Accessory: a pair of perforated 
tubercles very constant in occurrence, set. on the margins at the upper 
corners of the zocecia, and having nearly always in mature zoccia 
a.low semicircular extension. upwards, with a shallow pore at the 
change of level; they then combine with the zocecial margin to give 
a strong sug gestion of the upper half of a snake. (6) Vicarious: 
largish elliptical cells, with a long narrow aperture tapering slightly 
from head to foot, and constricted near the foot by two small paired 
1 Loe. cit., p. 98, pl. xi, fig. 2. 
