GEOGRAPHICAL DISTRIBUTION OF CRUSTACEA. 1555 



for the Leucosoids, 1 :2i. (The Arctic and Antarctic Seas are here 

 merged in the other kingdoms, with which they are most nearly 

 associated.) 



If we compare these ratios with those which the same groups sus- 

 tain as regards temperature, as exhibited on a former page, we discover 

 that there is a very close parallelism ; showing plainly that the preva- 

 lence of Maioids in the -Occidental Seas must be owing to the com- 

 parative prevalence of cold waters ; and the prevalence of the warm- 

 water groups, the Cancroids and Leucosoids, in the Oriental Seas, is 

 owing conversely to the great extent of warm waters. 



Again, the ratio between the A and B divisions together of the 

 Macroura, and the C division, is nearly as 1 : 0'8, which sustains the 

 same conclusion. 



The corresponding ratio for the Tetradecapoda is as 1 : 0'26. But 

 as this group, owing to the smallness of the species, has not been tho- 

 roughly investigated, except in European regions, directly under the 

 eyes of European observers, we cannot use satisfactorily the facts 

 they present for deducing general conclusions, or' for characterizing 

 zoological districts or provinces. Still, it should be observed that the 

 facts conform to the same principle. 



It is hence of the highest importance before comparing the zoolo- 

 gical character of different coasts, that the temperature-regions of 

 those coasts should be ascertained. 



Comparative tables of the East Indies and Mediterranean, or of the 

 Peruvian coast and the East Indies, or of the southeast and southwest 

 coast of Africa (and so on), would lead us far astray, if this element 

 were left out of view ; for a difference of temperature region, implies 

 a difference of genera and species, independent of other considerations. 

 On these grounds, whole continents, or sides of continents, may have 

 a common character and differ widely from other continents in the 

 same latitudes. 



If we look at the American continent in this point of view, we at 

 once perceive a striking peculiarity. All the coasts of North and 

 South America, with the Gallapagos on the west, belong to the Tem- 

 perate zone, excepting a few degrees along by Panama, and a con- 

 nected range of coast from Key West to Rio Janeiro. Chili and Peru 

 are excluded even from the warm temperate region, and so also, the 

 coast of the United States, north of Cape Hatteras. 



Now contrast America with the Oriental Seas. The whole east 



