THE BRACHIOPODA 21 



succession which has all the appearance of being an 

 actual genealogical tree, and as we pass back into the 

 earlier geological times we find a convergence of trie 

 lines of descent towards a few very simple forms. At 

 the beginning of the palaeontological record we seem to 

 be very near the beginning of the Brachiopoda. 



Classification must be based on structure and blood- 

 relationship. We cannot at this stage give a full justifi- 

 cation for the following classification (which is essentially 

 that of Beecher, 1893), but it is given as the best of 



^ \ 



FIG. 5. BATHONIAN TEREBRATULACEA. 



a, a', Epithyris bathonica S. Buckman, Bath oolite, x|; b, Ornithella 

 digona (J. Sowerby), Bradford clay, xf. (After Davidson.) 



many attempts to express the inter-relationships of 

 Brachiopoda. 



The Brachiopoda are so well defined and sharply 

 marked off from all other animals that they may well be 

 accorded the rank of a phylum or primary branch of the 

 Animal Kingdom.* Brachiopoda are marine animals 

 fixed by a pedicle or otherwise, feeding on microscopic 

 floating organisms by means of spiral " brachia," 



* Many zoologists unite the Brachiopoda with the Bryozoa in a 

 phylum Molluscoidea, of which they form two classes. The differ- 

 ences between them appear to the present writer too profound to be 

 expressed as merely class differences. 



