R. M. BrI/done — Fnrt/idr Notes' iaji the Ttimminghani, Chalk. 291 



be free to tloub.t whether jit ,ilnu§t:;iiiecessa;r.ily hold gopij iii the case 

 of specimens of widely differing, age. 'jFhe Polyzoa ai'e a particularly 

 good group in which to Jest this alleged persistence, of Cretaceous 

 forms into recent sea.>>,, for the complexify , of their .skeletons, at any 

 rate in the Cheilostomata, makeS: it ppssible to define an enormous 

 number of species, in fact all but th,© Iitxost primitive, with clearness 

 and certainty in a way unattainable in other groups. Now it 'is not 

 strongly marked species that ave; identified both iti recent- se.as- and 

 the Chalk, but primitive forms such vas .^/o)iia<oj;ora grmitkUuta ?i.\\(\. 

 Membranipora reticulum.', I ; atn not inclined to adhiit that -the 

 presence in the Chalk 0f Mfimhraniporcs whose skeleton can.iiot be 

 distinguished by any absolute chf),racter from tha,t of the reeeht 

 Jl. reticulum is conclusive or even presumptive evidence thdt polyps 

 identical with those of the recent M. reticulum lived in the Chalk 

 sea. It is not necessarily the case that because we habitually 

 assume that a simple polyp did not have a specialised skeleton we 

 are entitled to assume the converse that a specialised polyp did have 

 a specialised skeleton, or in other words that a simple cell like that 

 of M. reticulum could not be sufficient for the requirements of two or 

 inore differently organised polyps. There is nothing that I can see 

 to warrant this assumption, and until it can be supported by 

 stronger evidence it seems more pruderjt to continue to recognise 

 the great physical break between the Cretaceous and . Tertiary 

 epochs as a justification for refusing to admit the identity of 

 primitive Cretaceous forms with recent species. 



From the foregoing it will be gathered that I desire to see it 

 recognised as a principle that in dealing with the Cretaceous Polyzoa 

 we are not bound by the Tertiary and recent forms, and any strict 

 assimilation would be a priori injudicious, for it must be remembered 

 that the recent Cheilostomata with hard skeletons, the only ones 

 which can be compared with the Cretaceous Cheilostomata, may 

 fairly be considered to form a group in which the general lines of 

 development have long been settled, a middle-aged group. They 

 are, from the geological standpoint, absolutely contemporaneous, but 

 represent almost every possible variety of surroimding conditions. 

 The Cretaceous Cheilostomata, on the other hand, represent the 

 vigorous youth of the group when all sorts of experiments in 

 development were taking place, not only those which resulted in the 

 formation of stable families and genera which still exist, but also 

 those which produced such unstable and shortlived families as the 

 MelicertitidEe. They represent a long period, but on the whole only 

 one set of conditions. Under these circumstances it is only to be 

 •expected that rules which apply to one fauna will not always applj' 

 ■satisfactorily to the other. Differences which in one case were of 

 genuine specific importance might well in the other indicate merely 

 variations of a single species under the influence of distance in space 

 and variety of surroundings, and capable of being proved to be such 

 by a chain of intermediate forms. The importance of taki.ug such 

 considerations into account is exemplified by the history of Hageuow's 

 species Onycliocelln (CeUepora) Koninchiana. Hagenow gave two 



