486 RECENT BRACHIOPODA chap. 



The vertical range of depth of certain species is great ; Tei^e- 

 hratula vitrea is recorded from 5 to 1456 fathoms, T. Wyvillei 

 from 1035 to 2900 fathoms. This is to some extent expli- 

 cable since, after a certain depth has been reached, many of 

 the external conditions, such as absence of temperature and 

 light, must remain constant even to the greatest depths of the 

 ocean. 



The area of the ocean explored by dredging forms such an 

 infinitesimal fraction of the whole, that it seems superfluous to 

 consider the horizontal distribution of Brachiopods. A few 

 facts may, however, be mentioned. Certain species, as Terehra- 

 tula vitrea^ T. caput serpentis, Waldheimia cranium^ Megerlia 

 truncata^ and Discinisca atlantica^ have a very wide if not cos- 

 mopolitan distribution. The second of the above named extends 

 as far north as Spitzbergen, and as far south as Kerguelen 

 Island. Many species are, on the other hand, very localised, 

 and have hitherto only been found in one place. A very con- 

 siderable number of these have been dredged off Japan and 

 Korea, and this region may be to some extent regarded as the 

 headquarters of the group. 



The following species have been obtained within the limits 

 of the British Area, as defined by Canon Norman, who has been 

 good enough to revise the list, which is founded on that drawn 

 up by Davidson in his Challenger Report. Their range of 

 bathymetric distribution is given in the column on the left. 



Depth in 

 Fathoms 



to 1180. Terehratulina caput serpentis Lm. Oban, and off Cumbrae Islands, 



Loch Torridon, Scotland, off 

 Belfast 

 8 to 25. Terebratula (Gwijnia) capsula JeE. Belfast Bay, E. and S. coast of 



Ireland, Plymouth, Weymouth, 

 and Guernsey 

 5 to 690. Waldheimia cranium Mtiller . . North British seas. Off Shet- 

 land 

 75 to 725. Waldheimia septigera Loven . . North British seas. Off Shet- 

 land 

 TerebratellaspitzhergenensisT)-iiY. N.N.W. of Unst, Shetland 

 Argiope decollata Chemnitz . . Two miles east of Guernsey 

 Cistella cistellula S. Wood . . Shetland, near Weymouth, S. 



coast of England 



Atretia gnomon Jeff W. of Donegal Bay in 1443 



faths. Between Ireland and 

 Rockall, in 1350 faths. 



20 to 



600. 



18 to 



364. 



20 to 



45. 



050 to 1750. 



