308 DISTRIBUTION AND ETIOLOGY OF THE CRAYFISHES. 



cates by a narrow passage with the sea ; and also at Sta. 

 Cruz in the upper basin of the Rio Pardo, an affluent of 

 the Jaculiy, " bj' digging it out of holes in the ground." 

 The latter (P. hrasiliensis, fig. 64) was obtained at Porto 

 Alegre, and further inland, in the region of the primitive 

 forest at Rodersburg, in shallow streams. 



In addition to these, no crayfish have as j'et been 

 found in any of the great rivers, such as the Orinoko ; 

 the Amazon, in which thej' were specially sought for by 

 Agassiz ; or in the La Plata, on the eastern side of the 

 Andes. But, on the west, an "Astaciis" chilcnsis is 

 described in the " Histoire Naturelle des Crustacees," 

 (vol. ii. p. 333). It is here stated that this crayfish 

 "habite les cotes du Chili," but the freshwaters of the 

 Chilian coast are doubtless to be understood. 



Finally, Madagascar has a genus and species of cray- 

 fish (Astacoides madagascariensis , fig. 65) peculiar to itself. 



On comparing the results obtained by the study of the 

 geographical distribution of the crayfishes with those 

 brought to light bj' the examination of their morphological 

 characters, the important fact that there is a broad and 

 general corresi^ondence between the two becomes ap- 

 parent. The wide equatorial belt of the earth's surface 

 which separates the crayfishes of the northern from those 

 of the southern hemisphei'e, is a sort of geograi^hical 



fish. It is probably identical with the A.nohlUs of Dana and the -I. ar- 

 matiis of Von Martens. 



