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 

 1° 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 littoi'al 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 cliief factor governing the distri- 

 bution of marine Crustacea has been recognized by all writers on the subject. 

 In 1838 Milne Edwards t wrote : " I'etude de la distribution geographique 

 des Crustaces fait apercevoir aussi une coincidence remarquable enire la tempera- 

 ture des diverses regions carcinologiques et V existence ou la predominance de cer- 

 taines formes organiques. Ainsi, quoique les Crustaces des Antilles et des 

 mers de I'lnde soient tons ou presque tons d'especes differentes, ils ont entre 

 eux une analogic si grande, que les deux faunes offrent le meme aspect ge- 

 neral et se distinguent facilement de celles appartenant aux regions froides 

 de I'un et de I'autre continent. . . . Les regions temperees ont aussi entre 



* Bull. Mus. Comp. Zool., Vol. XXIII , No. 1, with maps, 1892. 

 t Ann. Sci. Nat., Zool., %" Ser., X. 150, 157. 



