[33] The nomenclature of the Australian crayfishes requires thorough revision. I therefore, for the present, assign no name to this crayfish. It is probably identical with the _A. nobilis_ of Dana and the _A. armatus_ of Von Martens. 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. 333). It is here stated that this crayfish “habite les côtes du Chili,” but the freshwaters of the Chilian coast are doubtless to be understood. Finally, Madagascar has a genus and species of crayfish (_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 apparent. 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 {310} representation of the broad morphological differences which mark off the _Potamobiidæ_ from the _Parastacidæ_. Each group occupies a definite area of the earth’s surface, and the two are separated by an extensive border-land untenanted by crayfishes. [Illustration: FIG. 77.—MAP OF THE WORLD, showing the geographical distribution of the Crayfishes. I. Eur-asiatic Crayfishes; II. Amurland Crayfishes; III. Japanese Crayfishes; IV. Western North American Crayfishes; V. Eastern North American Crayfishes; VI. Brazilian Crayfishes; VII. Chilian Crayfishes; VIII. Novozelanian Crayfishes; IX. Fijian Crayfishes; X. Tasmanian Crayfishes; XI. Australian Crayfishes; XII. Mascarene Crayfishes.]