BRITISH PAL^OGBNE BETOZOA. 229 



M. lacroixi (Aud.) [No. i, p. 240, pi. x. fig. 9]. M. eocena is more nearly allied to Mem- 

 branipora appendictdata (Eeuss), of which a good figure has been given by Mr. A. W. 

 Waters [No. 1 2, pi. ii. fig. 3], but from this it differs in that Reuss's species has a single 

 large avicularium on the lower side of the aperture and not quite in the median line ; 

 the opesia is also somewhat too large. M. macrostoma (Reuss) is another ally ; but 

 this has the rim that borders the opesia closer to the margin of the zooecia, so that the 

 flat depressed marginal space is absent. 



Species 2. Membkampoea buski, n. sp. 



Syn. Membranipora lacroixi, G. Busk (non Aud.), 1866, Geol. Mag. vol. iii. pi. xii. figs, lak, d; 

 (fide Vine), J. W. Judd, 1883, Geol. Mag. dec. 2, vol. x. p. 527; G. R. Vine, 1889, 

 Proc. Yorks. Geol. & Poh t. Soc. vol. xi. pt. 2, pp. 159-160, pi. v. fig. 2 (copied from Busk), 

 fig. 3 (original) ; H. W. Biistow, 1889, Geol. I. Wight, ed. 2, p. 284. 

 Membranipora reticulum, Vine (non Linn.), ibid. vol. xii. pt. 1, pp. 59, 60. 



Diagnosis. Zoari^tm encrusting or foliaceous. The back is flat and not ribbed. 



Zooecia arranged in long series. Opesia vei7 large : no lamina or fi-ont wall, the 

 raised rims of adjoining zooecia being in contact. The general form is oblong, the 

 length being not much greater than the width, except at the bifurcations of a row, 

 where the two zooecia are long and narrow. The raised rims are thick and plain. 



Avicularia irregularly scattered, small, generally in the lower right-hand comer of 

 the zooecia. 



Ocecia not always present, nanow, globose. 



Distribution. Headon Beds, Colwell Bay, I. of Wight ; London Clay, Highgate. 



%je. Brit. Mus. No. B 4625. 



Figures. PI. XXIX. tig. 11. Part of a zoarium with an ocecium ; X 55 diam. Brit. 

 Mus. No. B 4625. Fig. 12. Part of a specimen (Mus. Pract. Geol.) with ocecia, X 55 diam. 



Affinities. This species in its general characters very closely approaches M. lacroixi, 

 Aud. [No. I, p. 240, pi. X. fig. 9], and as such the London Clay specimen has been 

 fio-ured by Busk. With this identification I agreed until seeing the specimens in the 

 Museum of Practical Geology : these were collected by Mr. Chapman and are clearly 

 the same as those which he has kindly presented to the British Museum. They, however, 

 show the ocecia, and thus clearly separate the species from M. lacroixi, from which, 

 according to Mr. Hincks's diagnosis [No. 2, p. 130], these structures are absent. 



Species 3. Membkanipoka crassomuralis, n. sp. 



Diagnosis. Zoarium irregular, encrusting. 



Zooecia oval, irregularly distributed. Each zooecium surrounded by a thick prominent 

 rim. The interspaces between these rims are very narrow. When encrusting ribbed 

 bivalves the zocecia are more regularly arranged, running along the ribs or pressed into 

 the furrows. Opesia usually occupying the whole of the area, but in some a thin 



narrow lamina occurs. 



2l2 



