390 RL. M. Brydone—Chatk Polyzoa. 
II.—Norks oN NEW OR IMPERFECTLY KNOWN CHALK Potyzoa. 
By R. M. Bryponz, F.G.S. 
(PLATE XXX.) 
(Continued from the June Number, p. 260.) 
Ruacasostoma NovakiI, nom. noy. 
Syn. Wembranipora depressa, Novak, Denkschr. d. kais. Ak. d. Wiss. zu Wien, 
Math.-Naturw. Cl., Bd. xxxvii, p. 88, Taf. ii, figs. 9, 10. 
Novak considered this form within the range of variation of 
Cellepora depressa, Hag., but Canu’ recognizes it as a Rhagasostoma. 
It appears to be so closely related to a very distinct and persistent 
form which is very abundant and characteristic at Trimingham that 
I do not like to treat them as anything but two forms of a single 
hitherto unnamed species, and the form admirably figured by Novak 
must of course be the type of the species. 
Ruacasosroma Novak, mihi, var. Anetica, nov. Pl. XXX, Fig. 1. 
This is the above-mentioned form from Trimingham. It is dis- 
tinguished from Novak’s type by the squareness of the aperture, 
the much greater depth of the sinuses, and the general prevalence of 
a distinct inflexion of the sides of the aperture which makes the sinuses 
slightly bottle-shaped. The avicularia often show an interesting 
structure which would no doubt be found also in perfect specimens of 
Novak’s form; the sinus at the lower end of the aperture is closed by 
a narrow rectangular projection into the aperture just wide enough to 
seal up the sinus, and which is so deep-set as to appear to be not so 
much a process of the edge of the front wall as attached to its under 
surface. 
Very abundant at Trimingham; one specimen in zone of 
B. mucronata, Isle of Wight. 
CRIBRILINA CLAVICEPS, noy. Pl. XXX, Figs. 2-5. 
Zoarium always adherent. 
Zoecia very variable in size, length ‘68--9 mm., breadth 
*35—5 mm.; aperture variable in length and breadth, shaped like 
a keyhole, with a thickened margin round the upper part; what 
appear to be calcareous opercula may be sometimes seen inside the 
zocecia or even (Fig. 4) in situ; a pair of perforate tubercles often 
possessing a slight beak occur very regularly beside the aperture, and 
others occur somewhat irregularly on the edges of the front wall; — 
front wall slightly but decidedly keeled (Fig. 4), and showing ~ 
six or seven pairs of faint radiating imperforate furrows. 
Owcra not observed. 
Avicularia not observed except so far as the tubercles may be 
avicularian. 
Occurs regularly but sparingly in the Jf cor-anguinum zone at 
Gravesend and in Hants, and in the Marsupites zone in Hants. 
1 Bull. Soc. Géol. France, 1900, p. 428. 
