GEOGRAPHICAL DISTRIBUTION OF CRUSTACEA. 149Q 



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 several regions, in 

 order to discover what is the relation of the species to temperature, 

 and whether the cold or warm water species are the higher or lower 

 in grade, or whether the torrid or temperate zone can claim species of 

 the highest perfection or magnitude among the Brachyura. 



The following table gives the ratio which the number of species 

 of the several orders in the Temperate and Frigid zones, bears to that 

 of the Torrid zone. 



1. Maioidea, . . . . . . . 1 : 1-3 



2. Cancroidea, . . . . . . 1 : 3-3 



3. Grapsoidea, . . . . . . 1 : 2-1 



4. Leucosoidea, ... 1:2-0 



5. Corystoidea, . . . . . .1:0-3 



It hence appears that the Maioidea and Corystoidea are propor- 

 tionally much more abundant in the colder seas than the Cancroidea, 

 Grapsoidea, or Leucosoidea. 



If we examine into the subdivisions of the Maioidea and Cancroi- 

 dea, we shall find the differences between the two groups in distri- 

 bution more strikingly brought out. We shall find, moreover, that 

 both groups may be divided into a warm-water and cold-water section, 

 as below. 



I. MAIOIDEA. 



1. TEMPERATE ZONE SECTION. 



Torrid Temperate 

 species. species. 



1. Inaehidae, . . 1 



2. Maiidze, subfamilies Libininse, Maiinae, JPisinse, Otho- 



ninee, ....... 15 35 



3. Eurypodidae, ... 07 



4. Leptopodidse, 



17 00 



