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GENERAL CONSIDERATIONS ON THE DISTRIBUTION. 



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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 Pananui) to 110' 53' 4^' W. (Guaymas). An account of the topo- 

 graphy of tlie 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 loO 

 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 pccuhar 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 Edwards t wrote: "Yetudo de la distribution geographique 

 des Crustaccs fait apercevoir aussi une coincidence remarquahle entre la tempera- 

 hire des diverses regions careinologiqiics ct V existence ou la predominance de ccr- 

 taincs forw.es organiqites. Ainsi, quoique les Crustaces des Antilles et des 

 mers de I'Tnde soieni; tons ou presque tons d'especes differentes, ils out entre 

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

 neral et se distinguent facilement de cellos appartenant aux regions froides 

 de Fun et de Tautre continent. . . . Les regions temp6r6es ont aussi entre 



* J3ull. Mus. Cornp. Zo51., Vol. XXIIL, No. 1, with maps, 1802. 

 t Ami. Sci. NmI.., Zool., T Ser., X. 150, 157. 



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