40 TEE DEPTHS OF THE SEA. [chap. i. 



in which dredging has been attempted at any consider- 

 able depth, say 30 or 40 fathoms, that the number of 

 species common to the province dredged and to the 

 province to the north of it, is greatly increased 

 by the investigation being carried into a deeper zone. 1 

 Thus in the lusitanian province Mr. Mc Andrew 

 dredged off the coast of Galicia and Asturias, 212 

 species, 50 per cent, of which were common to the 

 coast of Norway ; and off the south of Spain 335 

 species were obtained, of which 28 per cent. w r ere 

 common to Norway (boreal province), and 51 per 

 cent, to Britain (chiefly Celtic province). The shells 

 common to the two or three provinces were chiefly 

 those dredged from considerable depths. The littoral 

 forms had a much more distinct aspect. The mollusca 

 of the ' Porcupine ' expedition have not yet been 

 thoroughly worked out. They are in the hands of 

 Mr. Gwyn Jeffreys, and his preliminary reports give a 

 most interesting forecast of what w r e may expect when 

 his labour is completed. He announces something 

 like 250 new species. Some of the more interesting 

 of these, and the general phenomena of their distri- 

 bution, will be referred to in a future chapter. 



The echinoderms of the expedition are more limited 

 in number, and have already been examined by the 

 writer with some care. The general distribution of 

 the Echinodermata is not so well known as that of the 

 Mollusca. There are many littoral and sub-littoral 

 species. Many of these are local, but many have a 

 wide geographical distribution, usually along what 

 Edward Eorbes calls a ' homoiozoic belt,' a belt of 

 nearly similar circumstances of climate extending 

 1 Woodward, loc. cit. p. .°)62. 



