398 R. M. Bnjdone~On Chalk Bnjozoa (Poli/zoa). 



III. — Notes on new ok impeefectly known Chalk Bryozoa (Polyzoa). 



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



(Continued from p. 339.) 



(PLATES XXII AND XXIII.) 



Membraniporella monastica, nov. PI. XXII, Figs. 1-3. 



Zoariiiyn always encrusting. 



Zocecia pyriform, average length, and breadth '43 mm. and "28 mm. ; 

 aperture semicircular, with a small tubercle at each side ; front wall 

 normally formed of five pairs of spines, the space between the lowest 

 pair being filled by a triangular plate perforated at the apex and 

 possibly tubular, as when it is broken off its base proves to be 

 perforated ; when there is a preceding zocecium with an ooecium the 

 fifth pair of spines and the triangular plate disappear, and the space 

 so left is filled by the preceding ooecium, which always carries a small 

 avicularium, possibly a relic of the triangular plate ; the spines are 

 not always strictly paired ; the backbone is often depressed and 

 pierced by irregular pores. 



Ooecia subquadrate, expanded above, free edge nearly straight. 



Avicularia. Besides the small avicularia on the ooecia there are 

 many independent avicularia scattered irregularly between the 

 zooecia ; they are long, narrow, and tumid, with triangular apertures, 

 and resemble a monk's cowl. 



The front wall is very fragile, and slight attrition will turn 

 a specimen into a spinose Memiranipora, but the avicularia and ooecia 

 will still enable its true nature to be recognized. 



Abundant at Trimmingham. 



Membraniporella castrxtm, nov. PL XXII, Figs. 4 and 5. 



Zoarium always encrusting. 



Zooecia deeply sunk inside an embankment of secondary structures, 

 average length and breadth -SS mm. and '33 mm. The primary form 

 appears to be shown in Fig. 4, at a, as slightly pyriform with a semi- 

 circular aperture and a front wall composed of from 13 to 16 radiating 

 and more or less paired spines, the first pair thickened and bearing 

 a stout triangular tooth projecting into the aperture. In the mature 

 form the walls and the lower lip of the aperture are strongly elevated 

 and tiny mandibular avicularia appear at the corners of the aperture, 

 and these structures blend with one another and the similar structures 

 of adjoining zooecia to form a large secondary aperture of irregular 

 shape and high enclosing wall round the front wall. From a depression 

 in the middle of the lower side of the lower lip of the secondary 

 aperture a broad bar with a median furrow descends gradually to the 

 front wall. 



Ooecia large, globose, projecting through the margin of the secondary 

 aperture, within which their free edges are sometimes visible. 



Avicularia. Besides the pair normally present at the corners of the 

 aperture, similar avicularia occur occasionally on the walls and round 

 the aperture. 



Fairly common at Trimmingham. 



