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 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 for 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 Crustacées,” 
(vol. ii. p. 383). It is here stated that this crayfish 
“habite les cétes 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, 
