U MAR 1 -'1917 %j 



THE - 



GEO LOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. IV. 



No. II.— FEBRUARY, 1917. 



ORICS-IHST-A-Il, .A.:RTIOIl.E!S. 



I. — Notes on new ok imperfectly known Chalk Polizoa. 

 By E. M. Brydone, F.G.S. 

 (Continued from Dec. VI, Vol. Ill, p. 435.) 

 (PLATE III.) 



Membkanipora crateroides, sp. nov. (PI. III. Figs. 1 and 2.) 



Zoarium unilaminate, incrusting. 



Zocecia large and pentagonal, average length, about - 8 mm., markedly 

 crater-shaped (i.e. with side walls sloping inwards to a deep-lying 

 ureal opening) : areas sub-pentagonal as a rule : side walls wide, 

 sloping inwards practically all the way from the zooecial margin, the 

 slope gentle in the lower half, then changing gradually to quite steep 

 at the upper end ; the two upper corners are occupied by a pair of 

 stumpy perforated tubercles; just below the summit of the steep 

 inward slope at the upper end of the arc, close to the corners and 

 probably communicating with the external tubercles, are two pores 

 so faint as to be hardly visible in full light. 



Ocecia very large even for zocecia of this size, and very globose ; the 

 only well-preserved specimens yet obtained have a jagged free edge 

 which probably was once straight or slightly concave. 



Avicularia very abundant; practically every zooecium that has not 

 an ocecium has above it a small, often sharply, equilaterally triangular 

 accessory avicularium with well-preserved crossbar; in addition 

 there are a number of sub-vicarious mandibular avicularia scattered 

 irregularly about, and ranging from fully developed forms about*45 mm. 

 in length with the upper part of the beak expanded and rounded off 

 down to forms about '3 mm. in length with a short blunt beak 

 projecting but little beyond a somewhat inflated body ; occasionally 

 these pass into a very remarkable form (Fig. 1) consisting of 

 a greatly inflated body embracing the whole of a short beak and 

 standing almost vertically on end. 



This species is distinguishable from II. trigonopora, Marss., 1 by its 

 sub-vicarious avicularia and perhaps its ocecia, as none are recorded 

 for Marsson's species, but they are obviously closely related. Like 

 the species described in the previous paper it is prominent in the 

 Weybourne Chalk ; but it also occurs in the Norwich Chalk. 



1 Loc. cit., p. 58, t. v, fig. 16. 

 decade vi. — vol. rv. — no. ii. 4 



