236 MR. J. W. GEEaOEY ON THE 



Affinities. This species diflers from the type species, Biselenaria placentula (Reuss), 

 in several important respects ; the most striking is that in the type there is a vibra- 

 cularium to every zooecium, situated just at the apex. This is practically the main 

 character used in the separation of Oupularia and Selenaria ; as in this case it is there- 

 fore generic, it might be thought that the two species ought to be separated into two 

 genera, one including B. placentula, corresponding to Cupularia, and one including 

 B. offa, corresponding to Selenaria. The two species, however, agree so closely 

 that it would appear to be unnecessary to make a new genus upon this character alone. 

 In merely specific points, the concavo-convex form of B. placentula, its more irregular 

 opesia, and the larger size and smaller number of its inferior zocecia all distinguish it 

 from B. offa. 



Family CRIBRILINID^. 

 Genus Cribkilina, Gray, 1848. 

 Diagnosis. Hincks, No. 2, p. 184. 



Species 1. Ckibrilina vinei, n. sp. 



Syn. Membraniporella nitida, Johnst. var. eocetia, G. R. Vine, Notes on Brit. Eoc. Polyzoa, 1889, 

 Proc. Yorks. Geol. & Polyt. See. vol. xi. pt. ii. pp. lGl-2, pi. v. fig. 6. 



Diagnosis. Zoarium encrusting. 



Zooecia large, quincuucially arranged ; globose. Orifice large, orbicular ; elongated 

 transversely. Margin of the orifice raised, thin and plain. 



The front walls of the zooecia are traversed by 9 or 10 pairs of furrows ; the upper 

 5 or 6 pairs of these are horizontal ; the lowest 3 or 4 pairs in a radial fan. There 

 are two or three pores in each furrow. The furrows do not reach the middle line of the 

 front wall, and upon this there is a varying number of fairly large pores. 



Avicularia large : a pair on each side of the orifice. 



Ooecia large : very globose, often covering the lower part of the adjoining zooecium.' 

 Perforated by numerous, fairly large pores. 



Distribution. London Clay, Sheppey. 



Type. Brit. Mus. No. B 4514. Vine Coll. 



Figures. PI. XXX. fig. 8. Part of the zoarium, X 55 diam. 



Affinities. This species was regarded by Mr. Vine as only a variety of the recent 

 Memhrani])orella nitida ; he remarked the presence of a series of small pores in the 

 furrows, and that Mr. Hincks did not mention them in his diagnosis of that species. 

 But the existence of these pores is the generic character that separates Crihrilina 

 from Memhraniporella, and into the former genus this species must necessarily go. 

 From the species to which Mr. Vine referred it, it diflfers also in the presence of the pores 

 on the ocecia, in that the lower furrows are radial instead of them all being horizontal, 



