BRACHIOPODA. 9 



The Brachiopods inhabit all the zones of vertical 

 depth. The Rev. M. J. Berkeley found a living speci- 

 men of Terebratula caput-serpentis attached to a rock 

 at low- water mark, on a part of the Scotch coast where 

 the tide falls only a few feet ; I have taken the same 

 species by dredging at various depths from 3 to 90 

 fathoms; M f Andrew and Barrett obtained T. cranium 

 alive at 160 fathoms; and Dr. Wallich has shown me 

 a shell of the last-named species which was brought 

 up by sounding off the east coast of Greenland in 228 

 fathoms. The nature of the sea-bottom, more than the 

 depth of water, determines the limit of their habitability. 



This class has two great and distinct types of form, 

 viz. the jointed and hingeless, although a fossil genus 

 (Davidsonia) is considered by M. Bouchard-Chantereaux 

 to form a connecting link between them. The above 

 distinction was first noticed and proposed by M. Des- 

 hayes, and it is founded on malacological as well as 

 conchological characters. By far the greater part of 

 the Brachiopoda (including the Terebratulidce) belong 

 to the former section, while the other comprises only 

 Crania, Lingula, and a few more genera. Both of 

 these types or sections are represented in the British 

 fauna. 



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