292 a. M. Brydone — Further Notes on the Trimminyham Chalk. 



figures of this species, and at first sight it would seem impossible 

 that they should belong to the same species. Gregory accordingly 

 gave to the second figure the specific name of Hagenoioi. This 

 involved the attribution to Hagenow of a careless blunder, but would 

 have been justifiable, as far as the creation of species from published 

 figures only can be justifiable, if Hagenow's specimens had come 

 from the settled conditions of ordinary Chalk. But they came from 

 the unsettled shallow- water conditions of the Maestricht Beds, where 

 unprogressive variation, as well as the progressive variation which 

 we call evolution, would be particularly likely to occur in the 

 Cheilostomata, and I have little doubt that Hagenow united his 

 figures in one species for the reason that I reunite them, namely, 

 that he had seen specimens responding accurately in different parts 

 to both figures. The species is evidently a variation which did not 

 prove advantageous and so did not lead to further developments, 

 and to which as a species from Maestricht we need not attach any 

 importance, but which, if it were to appear in recent seas, would 

 be a bombshell indeed. 



The recent genera Mucronella and Cribrilina do not give satis- 

 factory results when applied to the Cretaceous Polyzoa. In the 

 first place, the accepted definition of Crihrilina excludes species with 

 radiating or transverse furrows which are not punctured. There 

 does not, however, seem to be good ground for treating the presence 

 or absence of pores in the furrows (a point often very obscure in 

 fossil forms) as necessarily generic, and I propose for convenience to 

 treat the definition of the genus as extended accordingly. In the 

 second place, the two genera cover an enormous number of Cretaceous 

 species, and a study of these indicates that many of them possess 

 characters which would, if their front walls were not furrowed, 

 place them in entirely different genera and even families. Can such 

 forms be logically retained in a single genus? Certainly Crihriliua 

 and MembraniporeUa are not for the Cretaceous forms genera in the 

 same sense that, say, Mucronella and Porina are, but rather agglomera- 

 tions of the early stages of development of other families and geneia, 

 while the family and generic peculiarities were coming into existence, 

 and after they had come into existence, but while the development 

 of a fully calcified front wall was still incomplete. If the two 

 genera were dismembered a large number of species could be 

 successfully grouped with other families ; indeed, I think additions 

 out of the Cribrilinidfe would be made to nearly all the important 

 groups except the Celleporidee, Porinid^, and Hippothoidie, and it is 

 interesting to note that Jullien puts the two latter groups m 

 a separate suborder. Even if the Cribrilinidae are not dealt with in 

 this way the Cretaceous forms suggest that they are the product 

 of two totally distinct lines of development from the primitive 

 Membraniporidan cell. One of these lines is the commonly 

 recognised one, the arching over and fusion in the middle line of 

 marginal spines. But this will not satisfactorily account for the 

 very large number of species in which the front wall is attached 

 to the side of the side walls and does not rest on their surface. 



