Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/699

681 MARINE FISHES.] ICHTHYOLOGY 681 within which this fauna is comprised may be indicated 30 N. and S. lat., as in the Indo-Pacific. Its distinction from the Indo-Pacific lies in the almost entire absence of coral- feeding fishes. There are scarcely any Squamipinnes, Pharyngognaths, or Acronuridte, and the Teuthyes are entirely absent. The genera that remain are such as are found in the tropical zone generally, but the species are entirely different from those of the Indo-Pacific. They are mixed with a sprinkling of peculiar genera, consisting of one or two species, like Discopyge, Hoplopagrus, Doy- dixodon, but they are too few in number to give a strik ingly peculiar character to this fauna. Three districts are distinguishable, viz., the Central American, the Galapagos, and Peruvian. We add a few remarks on the first only. 1 That district shows so close an affinity to the Tropical Atlantic that, if the two were not separated by the neck of land uniting North and South America, they would most assuredly be regarded as em bracing a single fauna. With scarcely any exceptions the genera ars identical, and of the species found on the Pacific side nearly one-half have proved to be &quot;the same as those of the Atlantic. The explanation of this fact has been found in the existence of communications between the two oceans by channels and straits which must have been open till within a recent period. The isthmus of Central America was then partially submerged, and appeared as a chain of islands similar to that of the Antilles ; but as the reef-building corals flourished chiefly north and east of those islands, and were absent to the south and west of them, reef fishes were excluded from the Pacific shores when the communications were destroyed by the upheaval of the land. SOUTHERN TEMPERATE ZONE. This zone includes the coasts of the southern extremity of Africa from about 30 S lat., of the south of Australia, with Tasmania, and of New Zealand, and the Pacific and Atlantic coasts of South America between 30 and 50 S lat. The most striking character of this fauna is the reappear ance of types inhabiting the corresponding latitudes of the northern hemisphere, and not found in the intervening tropical zone. This interruption of the continuity in the geographical distribution of shore fishes is exemplified by species as well as genera, for instance Chimcera monstrosa, Galeus canis, Acanthias vulgaris, Acanthias blainvillii, Rhina sonatina, Ze us faber, Lophius piscatorius, Centriscus smlopax, Engraulis encrasic/iolus, Clu/&amp;gt;ea sprattus, Conger vulgaris. Instances of genera are still more numerous : Cestracion, Spinax, Pristiophorus, Raia ; Gallant hias, Polyprion, Histiopterus, Canthanis, Box, Girella, Pa- gellns, Chilndactyius, Sebastes, Aploactis, Agonus, Lepidopus, Cyttus, Psychrolutidce, Notacanthus ; Lycodes, Merlaccius, Lotdla, Phi/cis, Motel la ; Atilopus; Urocampus, Soleno- gnafhus, Alyxine. Naturally, where the coasts of the tropical zone are con tinuous with those of the temperate, a number of tropical genera enter the latter, and genera which we have found between the tropics, as well as in the temperate zone of the northern hemisphere, extend in a similar manner towards the sou Ji. But the truly tropical forms are absent ; there are no Squamipinnes, scarcely any Mullida 1, no Acronuri, no Teuthyes, no Pomacenlridoe (with a single exception on the coast of Chili), only one genus of Jididina, no Scarina, which are replaced by another group of Pharyn gognaths, the Odacina. The Labrina, so characteristic of the temperate zone of the northern hemisphere, reappear in a distinct genus (Malacopterus) on the coast of Juan Fer nandez. The family of Berycidce, equally interesting with regard 1 For the others the reader is referred to Giiiither s Introduction to the Study f Fishes, p. 280. to their distribution in time and in space, consists of tem perate and tropical genera. The genus by which this family is represented in the southern temperate zone (TracMchthys) is much more nearly allied to the northern than to the tropical genera. The true Cottiita and Heterolepidina (forms with a bony stay of the praeoperculum, which is generally armed) have not crossed the tropical zone ; they are replaced by fishes ex tremely similar in general form, and having the same habits, but lacking that osteological peculiarity. Their southern analogues belong chiefly to the family Trachinidce, and are types of genera peculiar to the southern hemisphere. The Discoboli of the northern hemisphere likewise have not penetrated to the south, where they are represented by Gobiesocidce. These two families replace each other in their distribution over the globe Nearly all the Pleuronectidce (but they are not numer ous) belong to distinct genera, some, however, being remarkably similar in general form to the northern Pleuro- nectes. With Gadoids Myxinidce reappear, one species being extremely similar to the European Myxine. Bdellostoma is a genus peculiar to the southern temperate zone. As in the northern temperate zone, so in the southern the number of individuals and the variety of forms is much less than between the tropics. This is especially apparent on comparing the numbers of species constituting a genus. In this zone genera composed of more than ten species are the exception, the majority having only from one to five. The proportion of genera limited to this zone is very high, about 65 out of a total number of 170 being peculiar to it. 1. The Cape of Good Hope district. Many of the genera found in this district are northern forms (Chimcera, Galeus, ScyUium, Acanthias, Torpedo, Haia, Dentcx, Cantharus, Box, Sagrus, Pay-rus, Pagcllus, Chrysophrys ; Sebastes, Sphyrcena . Lepidopus, Thyrsites ; Zeus ; Lophius ; Motclla), which in con junction with the peculiarly southern types (Callorhynchus, Chilo- dactylus, Agriopus, Clinus, Genypterus, Bdellostoma} leave no doubt that this district belongs to the southern temperate zone, whilst the freshwater fishes of South Africa are members of the tropical fauna. Only a few (Rhinobatus, Narchu, Astrape, and Sphyrocna) have entered from the neighbouring tropical coasts. The development of Sparoids is greater than in any of the other districts of this zone, and may be regarded as one of its distinguishing features. 2. The South Australian district comprises the southern coasts of Australia (northwards to about the latitude of Sydney), Tasmania, and New Zealand. It is the richest in the southern temperate zone, partly in consequence of a considerable influx of tropical forms on the eastern coast of Australia, where they pene trate farther southwards than would be expected from merely geographical considerations, partly in consequence of the thorough manner in which the ichthyology of New South Wales and New Zealand has been explored. Of the 120 genera hitherto found in this district 42 are peculiar. The shore fishes of New Zealand are not so distinct from those of south-eastern Australia as to deserve to be placed in a separate dis trict. &quot;With the exception of the genera which enter this zone from the tropics, and which are more numerous on the Australian coast than on that of New Zealand, and a few very local genera in addition, the remainder are identical. Many of the South Australian species, too, are found also on the coasts of New Zealand. The principal points of difference are the extraordinary development of Mon- acanthus on the coast of South Australia, and the apparently total absence in Australia of Gadoids, which in the New Zealand fauna are represented by 6 genera. 3. The Chilian district extends over 20 degrees of latitude only, and is nearly straight. In its northern and warmer parts it is of a very uniform character; it is there exposed to high and irngular tides, and to remarkable and sudden changes in the levels of land and water, which must seriously interfere with lislies living and pro pagating near the shore. No river of considerable size interrupts the monotony of the physical conditions, to offer an additional element in favour of the development of littoral animals. In the southern parts, where the coast is lined with archipelagoes, the climate is too severe for most fishes. All these conditions combine to render this district comparatively poor as regards variety of short fishes ; they belong to 45 genera, of which 6 only are not found ii XII. 86