is found, along with other blind animals, in the subterranean caves of Kentucky.

All the crayfishes of the northern hemisphere belong to the Potamobiidae, 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 Engaus 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,* 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 communi

*Südbrasilische Süss- und Brackwasser Crustaceen, nach den Samm. lungen des Dr. Reinh. Hensel. Archiv. für Naturgeschichte, xxxv. 1869.

* The nomenclature of the Australian crayfishes requires thorough revision. I therefore, for the present, assign no rame to this cray

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. 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

fish. It is probably identical with the A. nobilis of Dana and the A. armatus of Von Martens.

FIG 77.-MAP OF THE WORLD, showing the geographical distribution of the Crayfishes. 1. 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.

representation of the broad morphological differences which mark off the Potamobiida 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.

A similar correspondence is exhibited, though less distinctly, when we consider the distribution of the genera and species of each group. Thus, among the Potamobiida, Astacus torrentium and nobilis belong essentially to the northern, western, and southern watersheds of the central European highlands, the streams of which flow respectively into the Baltic and the North Seas, the Atlantic and the Mediterranean (fig. 77, I.); A. leptodactylus, pachypus, angulosus, and colchicus, appertain to the Pontocaspian watershed, the rivers of which drain into the Black Sea and the Caspian (I.); while Astacus dauricus and A. Schrenckii are restricted to the widely separated basin of the Amur, which sheds its waters into the Pacific (II.). The Astaci of the rivers of western North America, which flow into the Pacific (IV.), and the Cambari of the Eastern or Atlantic water-shed (V.) are separated by the great physical barrier of the Rocky Mountain ranges. Finally, with regard to the Parastacide, the widely separated geographical regions of New Zealand (VIII.), Australia (IX.), Madagascar (XII.), and South America (VI. and VII.), are inhabited by generically distinct groups.

But when we look more closely into the matter, it will