GEOGRAPHICAL DISTRIBUTION OF CRUSTACEA. 



the facts are not a little remarkable. One hundred fathoms appears 

 to have been the greatest depth of the Shetland dredgings. 



Now the temperature in the ^Egean during the warmer months, 

 according to Lieut. Spratt, is as follows : 



At the surface, . . 76-84. 



10 fathoms, seldom below 74 in the summer. 

 20 " " " 68 " " 



35 " " 62 " " 



75 " " " 56 " " 



100-300 " " " 55-55J " " 



The temperature of the waters near Southern England in summer 

 is 62; and near the Shetlands 55 or less. Consequently the surface 

 summer temperature of the British Channel is not found in the 

 JEgean at a less depth than thirty-five fathoms, and the surface 

 Hummer temperature of the Shetlands, is the temperature at one- to three 

 hundred fatJioms in the JEgean; and still species that range to a depth 

 of one hundred fathoms about Northern Scotland are found within 

 thirty fathoms of the surface in the .ZEgean, that is, where the summer 

 temperature is 74 or more. Such facts show the hardiness of the 

 species in enduring great ranges in temperature. We must, therefore, 

 conclude, that it is not temperature alone or mainly which determines 

 the depth to which species may live. It exerts an influence, and 

 species fitted for cold waters may be found in the deeper seas where 

 such waters occur; but the limit of descent depends on other in- 

 fluences. 



Looking at this table in another way, we see, as recognised by Prof. 

 Forbes, that species which occur at or near the surface in Northern 

 Scotland, are generally met with only at greater depths in the Medi- 

 terranean ; that is, the minimum depth is less in the former case than 

 the latter. Thus Corbula nucleus has for its minimum depth in the 

 Mediterranean six fathoms, and in the northern regions three fathoms. 

 Fbammobia ferroensis has ten fathoms for the former, and three for the 

 latter. Other examples will be found in the above table, sufficient to 

 illustrate the principle, although many exceptions exist. Thus species 

 that have the range of one hundred fathoms beyond Scotland, may 

 have the same in the Mediterranean, except that in many cases they 

 do not reach as near the surface, where the waters are warm. 



The Crustacea of the same seas illustrate this subject in a similar 



