CHAPTER X 



THE BRACHIOPODA 



I AM placing this group at the end of the mollusca. in 

 common with many others, but it is very certain that 

 they are not related to the mollusca. 



They have also for a long time been classed with the 

 Polyzoa and the ascidians, as Molluscoidea, but in accordance 

 with the most recent researches they must be placed in a 

 group by themselves, although they have some affinity with 

 the Polyzoa. 



These animals have a large body and a bivalve shell, 

 but the valves of the shell do not lie, as in the mollusca, 

 one on each side, but are placed dorsally and ventrally. 

 They have two coiled arms on the margin of the mouth. 

 These arms, or feet, as the name of the group implies, have 

 branchial functions that is, they are respiratory organs. 

 With the exception of one small species they are not 

 found in the littoral. They are better represented in the 

 Mediterranean and in southern seas than on our shores, 

 but one large species, the " Serpent's Head Shell " (Tere- 

 bratula caput serpentis), is found in the North Sea. 



Few and scattered at the present day, they abounded 

 in the primeval seas, and are a common fossil in Silurian, 

 Devonian, and other formations. 



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