THE 
GEOLOGICAL MAGAZINE. 
NEW SERIES...) DECADE, Wo... VOESS Vil. 
No. IV.— APRIL, 1910. 
ORIGINAL ARTICLIEHS. 
—_—_—_—_ 
I.—Norets oN NEW OR IMPERFECTLY KNOWN CHatk Potyzoa. 
By R. M. Brypong, F.G.S. 
(PLATE XIV.) 
(Continued from the February Number, p. 77.) 
Y next four species are linked together by their avicularia, which 
in each ease have the side walls infolded over a long deep-set area. 
MemeBranipora SAGITTARIA, noy. Pl. XIV, Figs. 1-3. 
Zoarium free or encrusting, always unilaminate. 
Zoecia elliptical; length of area -42 to 52 mm., with -48 mm. a fair 
mean; breadth -8 to °35mm.; the earlier specimens have practically 
common walls, the later ones show a progressive tendency to separation 
of the zocecia and sometimes a tendency to develop a second margin 
which reduces the area -29 to -31 mm. in length and -15 to -2mm. 
in breadth. 
Owcia very abundant but rather fragile, in the earlier specimens 
long and narrow, in the later ones showing a progressive tendency to 
broaden and fall back from the area. 
Avicularia of two types. (a) Accessory: in the zone of Mf. cor- 
anguinum small oblong rings lying at the head of the zocecium and 
occurring very regularly in pairs on either side of, and lying against, 
and slightly overlapping the occium, but nearly always failing to 
occur when a vicarious avicularium adjoins. In the specimen from. the 
lower part of the Actinocamax quadratus zone, shown as Fig. 2, they 
are developing in two directions, in one becoming exsert and over- 
lapping their surroundings, in the other sinking into the gradually 
deepening furrows between the zocecia and becoming mere triangular 
indentations; the latter line of development alone persists in the 
specimen from the upper part of the Act. quadratus zone shown as 
Fig. 3. (6) Vicarious: oblong cells with a long narrow elliptical 
aperture; there is a strong transverse bow-shaped ridge at the head 
of the cell, immediately below which the bounding walls are very 
sharply bent inwards until they overhang the aperture and almost 
meet in the middle line; they curve slowly back again and disclose 
a fairly wide front wall at the foot of the cell; just below the point 
at which they cease to overhang the aperture a pair of stout denticles 
are developed from the margin of the aperture. 
DECADE V.—VOL. VII.—NO. Iv. 10 
