W. D. Lang — Cretaceous Cheilostome Polyzoa. 497 



shown by Yine in his figure of the type-specimen. 1 Unfortunately 

 this specimen cannot be found; but a well-preserved paratype 

 specimen (from the same horizon and locality) exhibits the same 

 structure and shows that this is due to the collapse of the extra- 

 terminal front wall along a median line proximal to the aperture. 

 Other zocecia of the same specimen show the extra-terminal front wall 

 entire and a thin median seam — or rhamma — running proximally 

 from the aperture. The rhamma appears in some instances as a ridge 

 and in others as a depression ; in some zocecia it is not apparent ; and 

 when visible is extremely fine. In many cases the front wall is 

 broken along it (as in Vine's figure) and thus the rhamma. probably 

 indicates a line of weakness. It is suggested that the rhamma is 

 a ridge bounded by two furrows and that the front wall is thicker at 

 the ridge and thinner in the furrows. The rhamma, then, would 

 easily be broken off, and in such specimens a depression would appear 

 in its place; and a thin groove on each side would constitute a general 

 line of weakness which would account for the frequent breaking 

 down of the front wall. Owing to the extreme fineness of the 

 structure it cannot be definitely stated that that is the case. Vine 

 further records Membranipora gaultina from the Red Chalk of 

 Hunstanton 2 and from the Chalk Marl of Cambridge. 3 Specimens of 

 the former horizon only are in his collection, but similar forms from 

 the latter horizon have been obtained by washing by the late Mr. F. 

 Mockler and are in the British Museum. In each case the rhamma 

 is shown, though the specimens show differences from each other and 

 from the Gault form. Finally Mantell 4 figures and describes from 

 the Lower Greensand a uniserial Cheilostome possessing a rhamma 

 and obviously related to the Albian and Cenomanian forms. These 

 then may be grouped in a new genus ffliammatopora, with the 

 following diagnosis. 



Diagnosis. Incrusting, uniserial, Cheilostome Polyzoa with bilateral 

 branching ; 8 zocecia monomorphic, divided into a proximal caudal and 

 distal capitular portion ; termen 5 beaded ; extra-terminal front wall 5 

 well developed proximally and provided with a median seam or 

 rhamma which also appears to mark a line of weakness since the 

 extra-terminal front wall is often crushed in along this line; intra- 

 terminal front wall 5 represented by a narrow bevel, tending to 

 become broader proximally. 



Genotype. Membranipora gaultina, Vine. 



Distribution in time. Aptian to Cenomanian. 



Remarks. Of the three genera into which the species of ffliamma- 

 topora have been placed by various authors, Crisia is a Cyclostome 

 Polyzoan, Membranipora is multiserial and Mippothoa has a completely 

 calcareous intra-terminal front wall ; none possesses a rhamma. 



1 Vine, 1892, Proc. Yorks. Geol. Poly. Soc, new series, vol. xii, part 2, 

 pi. vi, fig. 15. 



2 Vine, 1890, loc. cit. 



3 Vine, 1890, op. cit., p. 461. 



4 Mantell, 1844, " Medals of Creation," p. 285, pi. Ixiv, figs. 3, 10, 106. 



5 For these terms, see Lang, 1914, Geol. Mag., Dec. VI, Vol. I, p. 6. 

 DECADE VI. — VOL. II. — NO. XI. 32 



