316 Geographical Distribution of Crustacea. 
vestigations. Still it cannot fail to be evident from a survey of 
the tables, that the line between the Torrid and Temperate zones 
is a natural zoological limit. 
If. The Torrid species of Brachyura (Torrid and Subtorrid 
Regions) greatly preponderate over those of the Temperate zone, 
the proportion being above two to one. This fact is the subject 
of remarks by Edwards, but with different conclusions from those 
_ which we would deduce. 
teen out of the thirty-nine species, or nearly one-half, occur in 
warmer temperate latitudes, only twenty species being confined 
to the Region 
_ Y. In the Torrid zone, the species of the torrid region, amount- 
ing to three hundred and forty-eight, exceed in number those of 
the Subtorrid by only forty-five, although the Subtorrid region is 
not one-third as great, both as to surface and extent of coast line. 
VI. Passing now from these general considerations respecting 
the Brachyura as a class to the several orders, we may look at 
their ratios among these orders and their subdivisions, for the sev- 
eral regions, in order to discover what is the relation of the ‘spe- 
cies to temperature, and whether the cold or warm-water species 
are the higher or lower in grade, or whether the torrid or the tem- 
perate zone can claim species of the highest perfection or magni- 
tude among the Brachyura. 
The following table gives the ratio which the number of spe- 
cies of the several orders in the Temperate and Frigid zones, 
bears to that of the Torrid zone. : 
1, Maioidea, eas : : bs 1: h3 
2. Cancroidea, - : : “ . - 1:33 
3. Grapsoidea, = - ‘ “ce é g is ~ 1:21 
4. Leucosoidea, < : ‘ “ s * 1; 20 
5. Corystoidea, = - - f 1:03 
__ It hence appears that the Maioidea and Corystoidea are propor- 
tionally much more abundant in the colder seas than the Cat- 
croidea, Grapsoidea, or Leucosoidea. 
