GEOGRAPHICAL DISTRIBUTION OF CRUSTACEA. 1485 



the distribution of reefs, it was easy to compare this temperature with 

 that of the greatest depths at which the proper reef corals occur. 

 This depth is but one hundred feet. Now the limiting temperature, 

 68, is reached under the equator at a depth of five hundred feet, and 

 under the parallel of 10 at a depth of at least three hundred feet. 

 There must, therefore, be some other cause besides temperature ; and 

 this may be amount of pressure, of light, or of atmospheric air dis- 

 solved in the waters. 



Prof. Forbes has remarked that the deep-sea species in the ^Egean 

 have a boreal character;* and Lieut. Spratt, also, has ascertained the 

 temperatures at different depths,f and shown that the deep-sea species 

 are those which have the widest range of distribution, most of them 

 occurring north, about the British shores or north of France. Yet is 

 it true that the species which occur in deep water in the ^Egean are 

 found in shallow waters of like temperature about the more northern 

 coasts? If so, Lieut. Spratt's conclusion, that temperature is the 

 principal influence which governs the distribution of marine fauna, in 

 depth as well as in latitudinal distribution, will stand as true. But 

 we believe that facts do not bear out this conclusion. Deep-sea 

 species live in deep seas in both regions, with but little difference in 

 the depth to which they extend. They are boreal in character, when 

 of Mediterranean origin, because they are cold-water species ; and 

 their wide distribution is because of the wide range of temperature for 

 which they are fitted, rather than their fitness to endure a given tem- 

 perature, which they find at considerable depths to the south, and 

 near the surface to the north. 



As this point is one of much importance, we have run over the 

 recent tables of dredging by Prof. E. Forbes, in the JEge&n and about 

 the British Islands,! to see how far it is borne out ; and we add other 

 results by R. Mac Andrew, Esq., at Vigo Bay, Portugal, Gibraltar, 

 Malta and Pantellaria, Algiers and Tunis. 



The great care and thoroughness of Prof. Forbes's researches and 

 those also of MacAndrew, give peculiar weight to the conclusions. 

 Those species are taken from the tables which are common to these 



* Keport on the .ffigean Invertebrata, Rep. Brit. Assoc., 1843, 130. 



f Rep. Brit. Assoc., 1848, 81. 



j Rep. Brit. Assoc., 1843; and on British Marine Zoology, ibid., 1850, 192. 



Rep. Brit. Assoc., 1850, p. 264. 



372 



