1486 



CRUSTACEA. 



several regions, and with regard to which the observations are free 

 from doubt; and we have confined the list to the Acephalous molluscs, 

 as these appear to be sufficient to test the law under discussion. The 

 depth is given in fathoms. 



It should be observed, that to carry out the theory, the species 

 should be confined to shallower waters to the north than to the south. 



To compare fairly this table, it should be noted that the dredging 

 at the Shetlands, Orkneys, and north of Scotland, was carried to a 

 greater depth than about Southern England, fifty fathoms being the 

 limit in the latter region, as the waters are shallow. Making this 

 allowance, we are still struck with the great depth to which the species 

 penetrate at the most northern locality, instead of the small depth. 

 Out of the twenty-one species which are here mentioned as occurring 

 on Northern Scotland, or the Shetlands, and the ^Egean, fourteen or 

 fifteen descend to a greater depth in the former than in the latter; and 

 nearly all the species common to the north and south extremities of 

 the British Islands, are reported from the deepest waters at the north. 

 Of the observations made at Vigo Bay, Malta, Pantellaria, Tunis, 

 Algiers, and Gibraltar, there is but a single example among the above 

 species of a greater range in depth than occurs in the northernmost 

 locality examined. The dredging in the Mediterranean by MacAn- 

 drew, was not carried to as great depths; yet even allowing for this, 



* Not found living at the depth stated. 



