212 MEMBRANIPOEA. 



Order CHEILO STOM AT A. 



Suborder ATHYBIATA. 



[Gregory. The British Palaeogene Bryozoa : Trans. ZooL Soc. vol. xiii. pt. vi. 



1893, p. 223.] 



Diagnosis. Cheilostomata with the front wall uncalcified or 

 incompletely calcified. 



Family HEMBRANIPORID^. 



Diagnosis. Athyriata with the front wall mainly membranous 

 and occupied by an opesial aperture, which does not correspond 

 to the operculum. The opesium is surrounded by a raised margin. 

 External ooecia. 



Genus MEMBRANIPORA, Blainville, 1834. 



Diagnosis. Membraniporidee in which the zoarium is a simple 

 erect or adnate sheet. The opesial aperture is generally of a 

 simple form, and the lamina is absent or but slightly developed. 



Membranipora jurassica, Gregory, 1894. 



Membranipora jurassica, Gregory, 1894, Jur. Cheil. : Geol. Mag. dec. 4, vol. ii. 



p. 62, fig. 1. 

 DIAGNOSIS : 



Zoarium erect, foliaceous, bilaminate. 



Zooecia regularly quincuncial, form hexagonal, slightly irregular. 

 Opesia very large. Aperture occupying the whole of the opesium 

 and markedly clithridiate in shape. Rim apparently plain, highest 

 on the margin of the aperture, and sloping thence to the inter- 

 zocecial sutures. Front wall very small in extent, consisting only 

 of a narrow space at the upper end of the zocecium, sometimes 

 replaced by ooecium. 



Ocecium cucullate, reniform in shape, surrounded by a low rim. 

 The ocecia are sparsely scattered over the zoarium. 



Avicularia usually a pair at the upper corners of the zocecium, 



