232 MK. J. W. GEE60RT ON THE 



Clay Bryozoan. M. laxa is a somewhat doubtful species ; it has not been referred to by 

 Mr. Waters [No. 12] in his recent revision. Eeuss's figure may only represent a 

 specimen in which the whole of the front wall is broken away and only the lateral walls 

 are left ; but if that is the case it is certainly not M. lacroixi, and in view of Pergens's 

 conclusion it would not be safe to act on this view. Eeuss's figure shows more regulai-ly 

 hexagonal zocecia ; the margins appear to be separated entirely by a narrow groove, 

 and there are no tubercles. Hence it seems safest to make a new species for this 

 London Clay form rather than to assert the existence of so doubtful a species as the 

 North Italian Bartonian M. laxa in the Lower Eocene of the London Basin. 



Species 5. Membranipora virgoliformis, n. sp. 



Diagnosis. Zoarium of elongate, cylindrical, solid shoots, somewhat resembling those 

 of Cellaria. 



Zocecia in regular longitudinal series, elongate, rectangular. Opesia large, oval, sur- 

 rounded by a thick raised and plain non-crenulate rim. A large depressed front wall 

 below the area, often with a pair of triangular depressions. 



Ocecia, none. 



Avicularia single, prominent, lateral, on the upper left-hand margin of the zocecia. 



Distribution. London Clay, Highgate. 



Type. Brit. Mus. No. 49658. Edwards Coll. 



Figure. PI. XXIX. fig. 8. Part of zoarium, X 25 diam. 



Affinities. In its mode of growth this species resembles M. sigiUata (Pourt.) 

 [No. I, p. 110 ; see also Smitt, No. 3, p. 8, pi. ii. figs. 64-68], but the zocecia in that 

 species are more irregular in form and distribution, while their general form is lozenge- 

 shaped instead of rectangular. It also recalls to mind M. monostachys. Busk [No. 2, 

 p. 31, pi. ii. fig. 2], but from this it difiers by the somewhat pyriform shape of the 

 zocecia and the more curved instead of flattened front wall of that species. 



Among the Lower Tertiary species, this most closely resembles Membranipora macro- 

 stoma (Eeuss) [Cellaria macrostoma, Eeuss, No. i, p. 64, pi. viii. figs. 5, 6; Bifinstra 

 macrostoma, Eeuss, No. 1 1, pp. 274, 275, pi. xxxiii. tigs. 12, 13], but in that the sub- 

 areal portion of the front wall is regularly rounded and has not the pair of triangular 

 depressions seen in the new species. 



Species 6. Membranipora disjuncta, n. sp. 



Diagnosis. Zoarium forming a large encrusting surface ; the zocecia are arranged in 

 disconnected rows, which are radially disposed ; there are several centres of radiation 

 in each zoarium. 



Zocecia elliptical ; opesia large, sun-ounded by a prominent rim ; the mouth opens 

 at one end of the opesium ; the rest is occupied by a thin calcareous lamina, 



Avicularia and ooecia unknown. 



