Geographical Distribution of Crustacea. 175 
If we compare these ratios with those which the same groups 
Sustain as regards temperature, as exhibited on a former page, we 
discover that there is a very close parallelism ; showing plainly 
that the prevalence of Maioids in the Occidental Seas must be 
_ owing to the comparative prevalence of cold waters; and the 
_ prevalence of the warm water groups, the Cancroids and Leuco- 
_ soids, in the Oriental Seas, is owing conversely to the grea 
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 as to the influence of temperature. 
__ 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 thoroughly investigated, except in European regions, di- 
rectly under the eyes of European observers, we cannot use sat- 
isfactorily 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 
zoological 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 Jead us far astray, 
if this element were left out of view ; for a difference of temper- 
_ ature region, implies a difference of genera and species, independ- 
_ ent 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 latitude. 
If we look at the American continent in this point of view, 
We at once perceive a striking peculiarity. All the coasts - 
perate region, and so also, the coast of the United States, north of 
Cape Hatteras. (See Chart, this Jour., vol. xvi.) : 
~ Now contrast America with the Oriental Seas. The whole 
1s room for many distinct provinces within the same temperature 
Tegion. The fact is more striking, if we consider that the At- 
