Distribution of Marine Species. 269 



The great care and thoroughness of Professor Forbes's re- 

 searches, and those also of Macandrew, give peculiar weight to 

 the conclusions. Those species are taken from the tables 

 which are common to these 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 oc- 

 curring in northern Scotland or the Shetlands, and the 

 iEgean, 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 ob- 

 servations 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 Macandrew was not carried to as great 

 depths ; yet even allowing for this, the facts are not a little 

 remarkable. 



Now, the temperature in the iEgean during the warmer 

 months, according to Lieut. Spratt, is as follows. 

 At the surface, 76° to 84°. 

 10 fathoms, seldom below 74° in the summer. 

 20 ... ... 68 



35 ... ... 62 



75 ... .., 56 



100 to 300 ... 55 to 55 J ... 



