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and exclusively an inhabitant of fresh water is as yet known to be found in distant continents, yet that in several other instances fishes identical in species (though not exclusively fresh-water) are found in the fresh waters of distant continents, and that very often the same genus is so distributed.

The genus Mastacembelus belongs to a family of freshwater Indian fishes. Eight species of this genus are described by Dr. Günther in his catalogue. These forms extend from Java and Borneo on the one hand, to Aleppo on the other. Nevertheless, a new species (M. cryptacanthus) has been described by the same author,2 which is an inhabitant of the Camaroon country of Western Africa. He observes : “The occurrence of Indian forms on the West Coast of Africa, such as Periophthalmus, Psettus, Mastacembelus, is of the highest interest, and an almost new fact in our knowledge of the geographical distribution of fishes."

Ophiocephalus, again, is a truly Indian genus, there being no less than twenty-five species, all from the fresh waters of the East Indies. Yet Dr. Günther informs me that there is a species in the Upper Nile and in West Africa.

The Acanthopterygian family (Labyrinthici) contains nine fresh-water genera, and these are distributed between the East Indies and South and Central Africa.

The Carp fishes (Cyprinoids) are found in India, Africa, and Madagascar, but there are none in South America.

Thus existing fresh-water fishes point to an immediate

See his Catalogue of Acanthopterygian Fishes in the British Museum, vol. iii. p. 540.

2 Proc. Zool. Soc. 1867, p. 102, and Ann. Mag. of Nat. Hist. vol. xx.

p. 110.

3 See Catalogue, vol. iii. p. 469.

connexion between Africa and India, harmonizing with what we learn from Miocene mammalian remains.

On the other hand, the Characinidæ (a family of the physostomous fishes) are found in Africa and South America, and not in India; and even the component groups of the family are so distributed,-namely, the Tetragonopterinal and the Hydrocyonina.2

Again, we have similar phenomena in that almost exclusively fresh-water group the Siluroids.

Thus the genera Clarias 3 and Heterobranchus 4 are found both in Africa and the East Indies. Plotosus is found in Africa, India, and Australia, and the species P. anguillaris) has been brought from both China and Moreton Bay. Here, therefore, we have the same species in two distinct geographical regions. It is however a coast fish, which, though entering rivers, yet lives in the sea.

Eutropius 6 is an African genus, but E. obtusirostris comes from India. On the other hand, Amiurus is a North American form ; but one species, A. cantonensis, comes from China.

The genus Galaxias 8 has at least one species common to New Zealand and South America, and one common to South America and Tasmania. In this genus we thus have an absolutely and completely fresh-water form of the very same species distributed between different and distinct geographical regions.

Of the lower fishes, a lamprey, Mordacia mordax," is common to South Australia and Chile; while another form

13.

i See Catalogue, vol. v. p. 311.
3 Ibid.
p.

4 Ibid. p. 21. 6 Ibid. p.52.

7 Ibid. p. 100. 9 Ibid. vol. viii. p. 507.

2 Ibid. p. 345.
5 Ibid. p. 24.
8 lbid. vol. vi.

P.

208.

of the same family, namely, Geotria chilensis, is found not only in South America and Australia, but in New Zealand also. These fishes, however, probably pass part of their lives in the sea.

We thus certainly have several species which are common to the fresh waters of distant continents, although it cannot be certainly affirmed that they are exclusively and entirely fresh-water fishes throughout all their lives, except in the case of Galaicias.

Existing forms point to a close union between South America and Africa on the one hand, and between South America, Australia, Tasmania, and New Zealand on the other ; but these unions were not synchronous any more than the unions indicated between India and Australia, China and Australia, China and North America, and India and Africa.

Pleurodont lizards are such as have the teeth attached by their sides to the inner surface of the jaw, in contra

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INNER SIDE OF LOWER JAW OF PLEURODONT LIZARD.
(Showing the teeth attached to the inner surface of its side.)

distinction to acrodont lizards, which have the bases of their teeth anchylosed to the summit of the margin of the jaw. Now pleurodont iguanian lizards abound in the South American region, but nowhere else, and are not as yet known to inhabit any part of the present continent of Africa. Yet pleurodont lizards, strange to say, are found in

i See Catalogue, vol. viii. p. 509.

Madagascar. This is the more remarkable, as we have no evidence yet of the existence in Madagascar of fresh-water fishes common to Africa and South America.

Again, that interesting island Madagascar is the home of very singular and special insectivorous beasts of the genera Centetes, Ericulus, and Echinops ; while the only other member of the group to which they belong is Solenodon, which is a resident in the West India Islands,

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Cuba and Hayti. The connexion, however, between the West Indies and Madagascar must surely have been at a time when the great lemurine group was absent; for it is difficult to understand the spread of such a form as Solenodon, and at the same time the non-extension of the active lemurs, or their utter extirpation, in such a congenial situation as the West Indian Archipelago.

The close connexion of South America and Australia is demonstrated on the Darwinian theory), not only from the marsupial fauna of both, but also from the frogs and toads which respectively inhabit those regions. A truly remarkable similarity and parallelism exist, however, between certain of the same animals inhabiting SouthWestern America and Europe. Thus Dr. Günther has described 1 a frog from Chile by the name of cacotus, which singularly resembles the European bombinator.

Again of the salmons, two genera from South America, New Zealand, and Australia, are analogous to European salmons.

In addition to this may be mentioned a quotation from Professor Dana, given by Mr. Darwin, to the effect that “it is certainly a wonderful fact that New Zealand should have a closer resemblance in its crustacea to Great Britain, its antipode, than to any other part of the world :” and Mr. Darwin adds, “Sir J. Richardson also speaks of the reappearance on the shores of New Zealand, Tasmania, &c., of northern forms of fish. Dr. Hooker informs me that twenty-five species of algæ are common to New Zealand and to Europe, but have not been found in the intermediate tropical seas.”

Many more examples of the kind could easily be brought forward, but these may suffice. As to the last-mentioned cases, Mr. Darwin explains them by the influence of the glacial epoch, which influence he would extend actually across the equator, and thus account for, amongst other

1 Proc. Zool. Soc. 1868, p. 482.
2 “Origin of Species,” 5th edition, 1869, p. 454.

3 Mr. J. J. Murphy, in a very interesting paper read before the Geological Society, June 9th, 1869, advances weighty reasons for believing that “the equatorial regions were never glaciated at all” (p. 355).

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