50 R. M. Brydone—Nevo Chalk Polyzoa. 



Membraniporella tjsniata, sp. nov. (PL III, Figs. 3 and 4.) 



Zoarium unilaminate, free or incrusting. 



Zo<scia very long, average length 1*2 to 1*3 mm., separated by 

 a broad common wall running like a continuous ribbon between the 

 lines of zooecia and expanding to a great width between successive 

 zocecia : front wall pierced by numerous pairs of long very slender 

 slits, the upper of which nearly meet in the middle line (in the early 

 stages, Fig. 4, they may be much wider), highly arched, and rising 

 steadily up to the greatly thickened final bar which forms the lower 

 lip of the aperture and is markedly V-shaped and rests on the side 

 walls distinctly beyond the areal margin : aperture large, roughly 

 circular, but with straight sides which pass under the lower lip at 

 a slight but distinct angle. 



Ocecia apparently absent, which indicates affinity with the Cribrilina 

 Gregoryi group. 



Avicularia occurring freely embedded in the common wall; the 

 great majority are of the small mandibular type characteristic of 

 Cribrilina Gregoryi, and are arranged roughly in pairs above and 

 below each aperture with others scattered about irregularly ; but 

 here and there occur much larger inflated and elongated forms with 

 the aperture wholly in the upper half. 



This species occurs in Hants in the upper part of the (restricted) 

 zone of A. quadratics, but is quite rare. 



Membraniporella bitobularis, sp. nov. (PI. Ill, Figs. 5 and 6.) 



Zoarium unilaminate, free or incrusting. 



Zocecia long and narrow, average length '8 to *9 mm. : side walls 

 often more or less distinct, but on the whole fused into a broad common 

 wall which spreads out to a great width at the foot of the zooecium 

 and slopes gently down to the aperture of the preceding zooecium : front 

 wall flatly arched, pierced by numerous pairs of slits of which about 

 the upper four are parallel and the remainder radiate, springing from 

 just inside the top of the side walls and rising from the foot to within 

 a short distance of the aperture, when it sinks again rather rapidly : 

 aperture terminal, heel-shaped, and deeply sunk, with the straight 

 lower lip thickened, but no thickened rim to the upper lip, much 

 overshadowed, together with the side wall for some way above it, by 

 lateral avicularia. 



Ocecia absent, as is only to be expected in a species with such 

 obvious affinity to Cribrilina Gregoryi. 



Avicularia very regularly present in pairs on either side of the 

 aperture as well as scattered irregularly along the side walls: the 

 apertural pairs might be regarded as single rather large rounded 

 accessory avicularia with abnormally stout crossbar in an unusually 

 central position, but I think it much more probable that they are 

 pairs of rudimentary avicularia in contact which have fused along the 

 contact, the lower one being as a rule distinctly the larger. 



This species is one of the very few which can be satisfactorily 

 recognized among the various forms of this group, small numerically 

 but great in variability, which occur in the M. cor-testudinarium zone 

 of Sussex. The two specimens figured, of which the original of 



