! 
" 
20 Geographical Distribution of Crustacea. 
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 Owue conversely to the Bes 
extent of warm waters. 
Again, the ratio between the A and B divisions tócoitis 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 "T'etradecapoda 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 lead 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 pna 
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 of 
North and South America with the Gallapagos on the west be- 
long to the 'l'emperate zone, excepiing a few degrees along by 
Panama, and a connected range of coast from Key West to Rio 
Janeiro. Chili and Peru are excluded even from the warm tem- 
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. 'lhe whole 
east coast of Africa, north of the parallel of 36? south, the coasts 
of India and the East India Islands, and the northern half of Aus- 
tralia, together with the numerous islands of the Pacifie, belong 
alike to the "T'orrid zone. In the American Seas, the torrid coasts 
make a single range, and have many species in common through- 
out. In the Oriental Seas, they reach with an uninterrupted sur-- 
face over one-half of the circumference of the globe, and there 
is room for many distinct provinces within the same temperature 
region. "Ihe fact is more striking, if we consider that the At- 
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