GENERAL CONSIDERATIONS ON THE DISTRIBUTION. 
THE route of the ‘ Albatross,” as will be seen by reference to the 
accompanying chart, traverses about twenty-nine degrees of latitude, from 
le S. (Galapagos Islands) to 28° N. (Guaymas, in the Gulf of California). 
In a longitudinal direction the region explored extends from 78° 34’ 20” W. 
(Gulf of Panama) to 110° 53’ 4” W. (Guaymas). An account of the topo- 
graphy of the region is given by Mr. Agassiz in his general sketch of the 
expedition.* The bathymetrical range explored is very great, extending 
as it does from the surface and the shore line to 2232 fathoms. 
In order to apprehend the faunal relations of the Crustacea of this region 
it will be convenient to consider separately the littoral and the deep-sea 
species. The littoral as distinguished from the deep-sea fauna may be taken 
to include the animals living between the shore and a depth of 100 to 150 
fathoms. But it must be borne in mind that there is no definite line divid- 
ing the littoral from the deeper fauna. In a general sense the depth speci- 
fied may be taken as that above which we find, but in a slight degree at 
most, those structural modifications which respond to the peculiar conditions 
obtaining at greater depths. 
That the temperature of the sea is the chief factor governing the distri- 
bution of marine Crustacea has been recognized by all writers on the subject. 
In 1838 Milne Edwardst wrote: “étude de la distribution géographique 
des Crustacés fait apercevoir aussi une comcidence remarquable entre la tempéra- 
ture des diverses régions carcinologiques et existence ou la predominance de cer- 
taines formes organiques. Ainsi, quoique les Crustacés des Antilles et des 
mers de I’'Inde soient tous ou presque tous d’espéces différentes, ils ont entre 
eux une analogie si grande, que les deux faunes offrent le méme aspect gé- 
néral et se distinguent facilement de celles appartenant aux régions froides 
de lun et de l’autre continent. . . . Les régions tempérées ont aussi entre 
* Bull. Mus. Comp. Zodl., Vol. XXTIL, No. 1, with maps, 1892. 
+ Ann. Sci. Nat., Zool., 2° Sér., X. 156, 157. 
