308 DISTRIBUTION AND iETIOLOGY OF THE CRAYFISHES. 



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

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

 the Jacuhy, " by digging it out of holes in the ground." 

 The latter (P. brasiliensis, 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 yet been 

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

 the Amazon, in which they were specially sought foi- by 

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

 Andes. But, on the west, an "Astacus" chilensis 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 by the examination of their morphological 

 characters, the important fact that there is a broad and 

 general correspondence 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 hemisphere, is a sort of geographical 



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

 matus of Von Martens. 



