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 the 

 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 



Fir,. 5. BATHONIAN TEREBRATULACEA. 



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

 digona (}. 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. 



