THE EUROPEAN SEAS. 



189 



Forms decrease in size from higher to deeper 

 regions, and in the same direction they part with 

 all their brilliant colouring and variety of pattern, 

 "Well-defined patterns are, with few exceptions, 

 presented only by Testacea inhabiting the littoral 

 and median zones. " In the Mediterranean one in 

 eighteen only of the shells undoubtedly belonging 

 to depths of 100 fathoms and upwards exhibited 

 any colour-markings, whilst the proportion of the 

 coloured to the colourless, from between thirty-five 

 to fifty-five fathoms, was as one to three." 



In our own seas the same species which are even 

 vividly coloured and banded in higher zones are 

 colourless when taken from depths below 100 

 fathoms ; a like absence of ornament takes place 

 proceeding northwards, at depths even of sixty 

 fathoms. 



Such is a brief and general outline of the change 

 which takes place in the Eastern Mediterranean, 

 from the surface to depths of upwards of 1300 feet. 

 Any lengthened enumeration of specific forms has 

 been purposely avoided. The features which are 

 noticed are only those broader ones which are de- 

 rived from positive characters. Each zone has a 

 distinctive sea-bed, with certain peculiar forms. As 

 we descend the dimensions of each zone become 

 greatly extended, so that whilst the upper has a 

 depth of only twelve feet, the lowest ranges through 

 700 feet. Specific animal forms decrease rapidly, 

 and just as the sub-aerial zones of vegetation pre- 



