CAINOZOIC FAUNAS 203 



is represented in the British Eocene, and again by such 

 large species as T. perforata in the East Anglian 

 Pliocene; but throughout the Cainozoic the Terebrat- 

 elloids seem to have favoured the clear and austral 

 waters that they now inhabit. Of Cainozoic Brachiopoda 

 it must be confessed that rarity makes them strati- 

 graphically negligible, and similarity to recent types 

 reduces their palaeontological interest. Reflecting upon 

 the overwhelming importance of the phylum in 

 Palaeozoic times, and the abundance of some groups in 

 the Mesozoic, it is impossible to repress the sentiment 

 contained in the hackneyed quotation Sic transit gloria. 



(H) MOLLUSCA 



Tertiary Mollusca have a definitely modern facies. 

 Not only are the proportionate values of the several 

 orders maintained without change from the Eocene to 

 the present day, but a great number of genera have 

 persisted throughout the era. Reduction and de- 

 generacy in the Cephalopoda are more than counter- 

 balanced by extreme diversity in Pelecypoda and 

 Gastropoda. The extraordinary abundance of terrestrial 

 forms of the latter order in modern faunas is probably 

 deceptive their choice of habitat denies them ordinary 

 chances of fossilization. But Teleodesmacean Bivalves 

 and Ctenobranchiate Univalves show a real increase 

 (foreshadowed in the Cretaceous period), and their 

 usual preference for muddy coastal water has enabled 

 them to leave abundant remains in British Cainozoic 

 deposits. 



Although Teleodesmacea are the predominant Pele- 

 cypoda of to-day, the old-established Prionodesmacea 

 are still important, and may even oust their more 

 progressive relatives locally. Taxodonts are represented 



