344 ME. p. W. HAEMEE ON THE LENHAM BEDS [Aug. 1 898, 



deep-water forms. Many of them have a wide bathymetrical range, 

 but, speaking generally, the fauna belongs, as has often been pointed 

 out, to the Coralline zone of Edward Porbes (15 to 50 fathoms), 

 although a few species characteristic of both deep and shallow water 

 are present. If, however, as I believe, the shells have been drifted, 

 the Coralline Crag fauna indicates the depth of the sea in which 

 the mollusca lived, rather than that of the deposit in which they 

 are embedded.^ 



Prestwich believed that the polyzoan fauna of the Coralline 

 Crag points generally to deep-water conditions, and he specially 

 instanced the genus Lepralia (of which many species, according 

 to Busk, occur in it) and some others, as characteristic of deep 

 seas. The classification of the Polyzoa has been much altered 

 of late years, but all the recent species described by Busk as 

 Lepralia are found at moderate depths, and he said of them that 

 they have perhaps a greater power of adaptation to different circum- 

 stances than is possessed by any other group of these animals.'^ 

 In a letter to Mr. Wood, Busk expressed his opinion that the 

 Crag polyzoa may have lived at any depth from the surface down- 

 wards,^ and with this opinion my son, who has paid much attention 

 to this subject, agrees. Mr. A. W. Waters states, it is true, that 

 in the Bay of Naples the Cyclostomata (polyzoa unprovided with 

 an operculum) are not, as a rule, found in shallow water, though 

 the Cheilostomata often are * ; but almost all the Crag forms 

 belonging to the first are of extinct species, of whose habits we 

 are ignorant, while the few living Crag species of the latter are said 

 to live in shallow as well as in deep water. Polyzoa are, moreover, 

 quite as abundant in the current-bedded portion of the upper part 

 of the formation, which Prestwich considered was deposited in 

 shallow water, as in those beds which he believed to have originated 

 at a greater depth. Many of the recent polyzoa have, like the 

 mollusca, a wide bathymetrical range, and, at least, it may be 

 said of the Crag forms that they lend little support to the deep- 

 water theory. 



No such depth as 500 to 1000 feet is known at present in the 

 southern part of the North Sea, nor in the English Channel. If 

 such a subsidence had occurred during the Crag period, it could 

 not have been local merely, but would have extended either in an 

 easterly or a westerly direction. In the one case it would have 

 caused the submergence of the Miocene beds of North Germany, in 

 the other it would have carried the sea over a great part of the 

 midland counties of England ; but of such extensions of the German 

 Ocean during the Pliocene period there is no evidence, and they 



^ On the Turbot Bank, off the Antrim coast, to which reference will be made 

 hereafter, a few deep-water species were found, dead, in 25 to 30 fathoms, which 

 were afterwards discovered living in a deeper and adjoining part of the Irish Sea. 



2 ' Crag Polyzoa,' Monogr. Palseont. Soc, 1859, p. 38. 



^ Suppl. ' Crag. Mollusca,' Introd. p. v, Monogr. PalaBont. Soc. 1872. 



* Quart. Journ. Geol. Soc. vol. xl (1884) p. 681. 



