Thus, on the continent of the old world, the crayfishes are restricted to a zone, the southern limit of which coincides with certain great geographical features; on the west, the Mediterranean, with its continuation, the Black Sea; then the range of the Caucasus, followed by the great Asiatic highlands, as far as the Corea on the east. On the north, though there is no such physical boundary, the crayfishes appear to be entirely excluded from the Siberian river basins; while east and west, though a sea-barrier exists, the crayfishes extend beyond it, to reach the British islands and those of Japan.
Crossing the Pacific, we meet with some half-a-dozen kinds of crayfishes,[30] different from those of the old world, but still belonging to the genus Astacus, in British Columbia, Oregon, and California. Beyond the Rocky Mountains, from the Great Lakes to Guatemala, crayfishes abound, as many as thirty-two different species having been described, but they all belong to the genus Cambarus (fig. [63], p. 248). Species of this genus also occur in Cuba,[31] but, so far as is at present known, not in any of the other West Indian islands. The occurrence of a curious dimorphism among the male Cambari has been described by Dr. Hagen; and a blind Cambarus {306} is found, along with other blind animals, in the subterranean caves of Kentucky.
[30] Dr. Hagen in his “Monograph of the North American Astacidæ,” enumerates six species; A. Gambelii, A. klamathensis, A. leenisculus, A. nigrescens, A. oreganus, and A. Trowbridgii.
[31] Von Martens. Cambarus cubensis. Archiv. für Naturgeschichte, xxxviii.
All the crayfishes of the northern hemisphere belong to the Potamobiidæ, and no members of this family are known to exist south of the equator. The crayfishes of the southern hemisphere, in fact, all belong to the division of the Parastacidæ, and in respect of the number and variety of forms and the size which they reach, the head-quarters of the Parastacidæ is the continent of Australia. Some of the Australian crayfishes (fig. [76]) attain a foot or more in length, and are as large as full-sized lobsters. The genus Engæus of Tasmania comprises small crayfish which, like some of the Cambari, live habitually on land, in burrows which they excavate in the soil.
New Zealand has a peculiar genus of crayfishes, Paranephrops, a species of which is found in the Fiji Islands, but none are known to occur elsewhere in Polynesia.
Two kinds of crayfish have been obtained in southern Brazil, and have been described by Dr. v. Martens,[32] as A. pilimanus and A. brasiliensis. I have shown that they belong to a peculiar genus, Parastacus. The former was procured at Porto Alegre, which is situated in 30° S. Latitude, close to the mouth of the Jacuhy, at the north end of the great Laguna do Patos, which {308} communicates 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.
[32] Südbrasilische Süss- und Brackwasser Crustaceen, nach den Sammlungen des Dr. Reinh. Hensel. Archiv. für Naturgeschichte, XXXV. 1869.
FIG. 76.—Australian Crayfish (1⁄3 nat. size).[33]