4 Geographical Distribution of Crustacea. 
 vestigations. Still it cannot fail to be evident from a survey of 
the tables, that the line between the 'l'orrid and 'l'emperate zones 
is a natural zoological limit. 
II. The 'l'orrid species of Brachyura ('T'orrid and Subtorrid 
Regions) greatly preponderate over those of the 'l'emperate zone, 
the proportion being above two to one.  'T'his fact is the subject 
of remarks by Edwards, but with different conclusions from those 
which we would deduce. 
III. 'T'he Frigid zone, as far as known, includes one species 
peculiar to it, the CZonccetes opilio. And Stenorhynchus pha- 
langium, Hyas araneus, Portunus pusillus, Carcinus menas, 
and Cancer pagurus, are all that are known to extend into it 
from the Temperate zone. Perhaps the Cancer chirogonus from 
Kamtschatka ( T'elmessus chirogonus of White) should be added. 
''his may be in part evidence of the little exploration hitherto 
made in the Frigid Seas. Yet, after the investigations of Beechey, 
Fabricius, Kroóyer, Rathke, and others, we may be assured that 
the number of species 1s exceedingly small. 
IV. Within the TTemperate zone, the species are most numer- 
ous in the Warm Temperate, ''emperate, and Subtemperate Re- 
gions; beyond this, the number diminishes, being a quarter less 
in the Cold 'T'emperate than in the Subtemperate, and Aaíif less 
in the Subfrigid. Moreover, in the last-mentioned region, seven- 
teen out of the thirty-nine species, or nearly one-half, occur in 
warmer temperate latitudes, only twenty species being confined 
to the Region. 
V. 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 'l'emperate and F'rigid zones, 
bears to that of the 'l'orrid zone. 
1. Maioidea, - - . - - - - d E 
2. Cancroidea, - - - - - - 1:98 
3. Grapsoidea, - - - - - . : 01:24 
4. Leucosoidea, - - - - - - 1:2:0 
5. Corystoidea,  - - - E: E - - 1:038 
It hence appears that the Maioidea and Corystoidea are propor- 
tionally much more abundant in the colder seas than the Can- 
croidea, Grapsoidea, or Leucosoidea. 
