32 THE CRAG POLYZOA. 



Habitai. — C. Crag, on shell, S. W. 



Though placed among the MemhraniporcB, it is extremely doubtful whether the 

 fragment here described be a Membranipora, or even a Polyzoon at all. If so, it should 

 perhaps form the type of a new genus or even family. 



§ 2. Armat^. 

 5. M. TRiFOLiuM, S. Wood. PI. Ill, figs. I, 2, 3, 9. 



Polyzoario discoidali, radiato, diffuso ; cellulis elongatis, rhomboidalibus seu hexagonis ; 

 aviculario unico vel duobus in fronte cellulae infra posito ; ovicellula aream depressam 

 triangularem ostendente. 



Polyzoarium discoidal, radiate, indefinite, cells elongated, rhomboidal or hexagonal ; 

 one or two avicularia on the lower part of the cell in front within the area ; surface 

 smooth ; ovicell with a triangular depression in front. 



M. TEiroLiUM, S. Wood, Ann. Nat. Hist., xiii 



Habitat. — C. Crag, on Terebratula grandis, and other shells ; very abundant. Red 

 Crag (?) 8. W. 



The peculiar trifoliate shape of the aperture at once distinguishes this species from all 

 the other fossil Memhraniporce of the Crag, as well as from all living species with which I 

 am acquainted, except, perhaps, M. Flemingii. 



The avicularia are not always present, and instead of one in the median line on the 

 front of the cell, there may be two, one on either side, arising apparently in the line of 

 division between two cells. The double avicularia are usually found on those parts of the 

 polyzoarium in which the ovicells exist ; the latter consequently are commonly, if not 

 always, seen to be crowned, as it were, with two avicularia, one on either side of the 

 summit, as is often the case also in the recent M. Flemingii. 



The only Red-Crag specimen which appears to belong to this species is too imperfect 

 to allow of its identity being positively determined. 



6. M. PouiLLETii, Audouin. PI. Ill, figs. 4, 5, 6. 



Cellulis ovatis, deorsum latioribus ; lamina ; margine granuloso, tenui ; supra, 

 4- — 6 spinis armato. Aviculariis sparsis seu subinde aviculariio utroque lateri ovicellulae 

 posito. 



