THE EUROPEAN SEAS. 



177 



bceus, &c. Had this local assemblage been more 

 numerous it would have been interesting to have 

 traced its extra-Mediterranean relations ; but, small 

 as it is, it would not be without its value if all the 

 species pointed to some common province or loca- 

 lity ; but such is not the case. Two of the Cassi- 

 darice are old occupants of the great Mediterranean 

 basin.; and though Dolium galea is found in the 

 Red Sea, it by no means follows that it came from 

 thence, inasmuch as, together with Umbrella, it has 

 a wide distribution in the South Lusitanian Atlan- 

 tic Province, and is also one of the old Mediterra- 

 nean fossil forms. 



From some observations made in the neighbour- 

 hood of Algiers, it was found that through all the 

 months of the year the temperature of the water 

 decreased from the coast-line outwards, as also from 

 the surface downwards ; this decrease is greater in 

 summer than in winter. The temperature of the 

 water is higher than that of the air in autumn and 

 winter, lower in spring and summer. In the deeper 

 zones it falls as low as 54° F., which it never passes, 

 as has been ascertained for depths of from sixty 

 to 360 fathoms. 



The mean winter temperature of Toulon is 52° 

 F., that of Algiers 58° F., the mean being 54° ; in 

 the Adriatic the mean temperature of the air is. 

 between 59° F. and 73° F., that of the water being 

 between 66° F. and 71° F. The difference is not 

 great, but, so far as temperature can influence the 



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