202 INVERTEBRATE PALAEONTOLOGY 



spicuous than the massive surface-dwellers. Schizaster 

 (which occurs in local clusters in the London Clay) 

 competes with the Cretaceous Hemiaster in specific 

 differentiation (PI. xv. fig. 2), while Brissus^ Brissopsis-> 

 Echinocardium, Moira and Spatangus help to prove the 

 continuity of Cainozoic with recent faunas. 



(F) POLYZOA 



The most noteworthy assemblage of Polyzoa in 

 British Tertiary strata is that of the Coralline Crag of 

 the East Anglian Pliocene. Cyclostomata are there 

 represented by massive colonies of Theonoa, Alveolaria 

 and Hornera, but they are inferior in numbers to the 

 Cheilostomata, of which Retepora is the most familiar 

 genus. This proportion of the two important orders 

 of Gymnolaemata is that normal to Tertiary faunas. 

 Apart from the Crags, Polyzoa are rare in the 

 argillaceous or sandy deposits of the British Tertiary, 

 but at the present day Membranipora and Flustra 

 abound in shallow water around the coasts. 



(G) BRACHIOPODA 



The only series of Brachiopoda to show any phyletic 

 vigour in Cainozoic times is that of the Terebratulacea, 

 and among them the Terebratellids (the latest group 

 to arise) alone attain faunal prominence. It may be 

 confidently assumed that the abundance of recent 

 genera recognized in this section is the outcome of more 

 complete morphological knowledge, and will sink into 

 relative insignificance as continued study is applied to 

 fossil types. 



The Lingulids, Thecidiidae and Craniidae continue 

 their unaspiring progress throughout the era, and the 

 Rhynchonellids are hardly more important. Terebratula 



