DISTRIBUTION OF BKACHIOPODA. 253 



Corea, Florida, is of frequent occurrence, and not unlikely certain 

 species may be even restricted to special bays or inlets of the sea. 

 But few other than boreal or hyperboreal species are found inhabit- 

 ing opposite sides of the same oceanic basin; notable exceptions 

 are Platydia anomioides, whose range embraces the Mediterranean 

 and West European coasts and the Florida reefs, and Thecidium 

 Mediterraneum, from the northwest coast of Africa and Jamaica, 

 both with a vertical range falling within six hundred fathoms. The 

 most striking instances of areal discontinuity are furnished by 

 Terebratella Frielii (near Halifax, one thousand three hundred and 

 forty fathoms, and the Philippine Islands, one hundred and two 

 fathoms) and Discinisca stella (Singapore, Philippines, Japanese and 

 Chinese seas, and Bermuda), the former a deep-sea species, and the 

 latter restricted to shallow water (seventeen to forty-nine fathoms). 

 From such data as have been given, it would appear that the 

 oceanic abysses form an insuperable barrier to the passage of the 

 Brachiopoda ; how the transference was effected in the case of the 

 few exceptional species that have been indicated remains a matter 

 of conjectm'e. 



In their bathymetrical distribution the Brachiopoda affect the 

 most diverse conditions of existence. While some forms (all or 

 nearly all the species of Lingula, for example) appear to be incapa- 

 ble of living in greater depths than a few fathoms below water-line, 

 othars, again, seem just as incapable of leaving the greater depths. 

 Discinisca Atlantica, a widely spread deep-sea species, has thus far 

 been found only in water exceeding six hundred and fifty fathoms, 

 and Terebratula Wyvillii, an equally wide-spread and abundant 

 species, in water exceeding one thousand fathoms. Other species, 

 on the other hand (Terebratula vitrea, 5-1456 fathoms ; Terebratu- 

 lina caput-serpentis, 0-1180 fathoms), seem capable of accommo- 

 dating themselves to the greatest variety of depths. The species 

 exhibiting the widest range of accommodation are such as have in 

 part a boreal or arctic habitat ; in other words, forms which find 

 the same water-temperature at the surface and at varying depths 

 beneath the surface. Per contra^ the species having the most lim- 

 ited vertical range are those confined to the warm waters, tropical 

 and sub-tropical. From this it follows that distribution in depth is 

 effected primarily by conditions of temperature, and not by consid- 

 erations of light, food-supply, &c., as has been urged by Fuchs and 



