Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/700

682 682 ICHTHYOLOGY [DISTRIBUTION. other district s of this zone. Three are peculiar, viz., Mcndosoma, Myxodes, and Malacoptcrus ; Porichthys&n&Agonus&vu penetrated thus far southwards from the Peruvian and Californian districts; and Polyprion is one of those extraordinary instances in which a very specialized form occurs at almost opposite points of the globe, without having left a trace of its previous existence in, or of its passage through, the intermediate space. 4. Our knowledge of the fauna of the Patagonian district is, with the exception of the neighbourhood of the mouth of the Rio de la Plata, in too fragmentary a state to deserve further notice here. ANTARCTIC OCEA.N. To this fauna we refer the shore fishes of the southernmost extremity of South America, from 50 S. lat., with Tierra del Fuego and the Falkland Islands, and those of Kerguelen s Land, with Prince Edward s Island. No fishes are known from the other oceanic islands of these latitudes. In the southern hemisphere surface fishes do not ex tend so far towards the pole as in the northern ; none are known beyond 60 S. lat., and the Antarctic fauna which is analogous to the Arctic inhabits coasts more than ten degrees nearer to the equator. It is very probable that the shores between 60 and the Antarctic Circle are inhabited by fishes sufficiently numerous to supply part of the means of subsistence for the large seals which there pass at least some portion of the year, but hitherto none have been obtained by naturalists ; all that the present state of our knowledge justifies us in saying is, that the general char acter of the fauna of Magellan s Straits and Kerguelen s Land is extremely similar to that of Iceland and Greenland. As in the Arctic fauna, Chondropterygians are rare, and are represented by Acantkias vidgaris and species of Raia. Ilolocephali have not yet been found so far south, but Callorhynchus, which is not uncommon near the northern boundary of this fauna, may prove to extend into it. As to Acanthopterygians, Cataphracti and Scorpcenidce are represented as in the Arctic fauna, two of the genera (Sebastes and Agonus) being identical. The Cottidce are replaced by six genera of Trachinidce, remarkably similar in form to Arctic types; but Discoboli and the characteristic Arctic Blennioids are absent. Gadoid fishes reappear, but are less developed ; as usual they are accompanied by Myxine. The reappearance of so specialized a genus as Lycodes is most remarkable. Flat fishes are few as in the north, and belong to peculiar genera. Physostomes are probably not entirely absent, but hitherto none have been met with so far south. Lopho- branchs are rare, as in the Arctic zone ; it is noteworthy, however, that a peculiar genus, with persistent embryonic characters (Protocampus), is rather common on the shores of the Falkland Islands. Pelagic Fishes. ^ Pelagic fishes, that is, fishes inhabiting the surface of mid-ocean, belong to various orders, viz., Chondropter ygians, Acanthopterygians, Physostomes, Lophobranchs, and Plectognaths. Neither Anacanths nor Pharyngognatlis con tribute to this series of the marine fauna. The following genera and families are included in it : Chondropteryffii.C&rch&Tias, Galeocerdo, Thalasso- rhinus, Zygaena, Triaenodon, LamnidfB, Rhinodon, Notida- nidae, Laemargus, Euprotomicrus, Echinorhinus, Isistius ; Myliobatidse. _ Acanthopterygii. Dactylopterus, Micropteryx, Scom- brina, Gastrochisma, Nomeus, Centrolophus, Coryphaenina, Seriola, Temnodon, Naucrates, Psenes, Xiphiidae, Anten- narius. Physoslomi. Sternoptychidae, Scopelus, Astronesthes, Scombresocidae (majority). Lophobranchii. Hippocampus. Plectognathi. Orthagoriscus, and some other Gymno- donts. Pelagic fishes differ much from one another in their mode of life. The majority are excellent swimmers, which not only can move with great rapidity, but are also possessed of great powers of endurance, and are thus enabled to COR. tinue their course for weeks, apparently without the neces sity of rest ; such are many sharks, scombroids, dolphins, pilot-fish, sword-fishes. In some, as in Dactylopterus and Exoc.(tus, the ability to take flying leaps out of the water is superadded to the power of swimming (flying-fishes). But in others the power of swimming is greatly reduced, as in Antennarius, Hippocampus, and Gymnodonts ; they frequent places in the ocean covered with floating seaweed, or drift on the surface without resistance, at the mercy of wind and current. The Echeneis or sucking-fishes attach themselves to other large fishes, ships, or floating objects, and allow themselves to be carried about, unless change of climate or want of food obliges them to abandon their temporary carrier. Finally, another class of pelagic fishea come to the surface of the ocean during the night only ; in the day time they descend to some depth, where they are undisturbed by the rays of the sun or the agitation of the surface-water ; such are Brama, the Sternoptychidce^ Scopelus, Astronesthes, fishes the majority of which are provided with those extraordinary visual organs that we find so much developed in the true deep-sea fishes. Indeed, this last kind of pelagic fishes constitutes a connecting link with the deep-sea forms. Pelagic fishes, like shore fishe&quot;s, are most numerous in the tropical zone ; and, with few exceptions (Echinorhinus, Psenes, Sternoptychidce, Astronesthes), the same genera are represented in the tropical Atlantic as well as in the Indo-Pacific. The number of identical species occurring in both these oceans is great, and probably still greater than would appear from systematic lists, in which there are retained many specific names that were given at a time when species were believed to have a very limited range. The pelagic fauna of the tropics gradually passes into that of the temperate zones, only a few genera, like Cybium, Psenes, Antennarius, being almost entirely confined to the tropics. All the other tropical genera range into the temperate zones, but their representatives become fewer with the increasing distance from the equator. North of 40 N. lat. many genera have disappeared, or are met with in isolated examples only, as Car chart as, Zygcena, Notidanus, Myliobatidce, Dactylopterus, Echeneis, Nomeus, Coryphtxna, Schedophilus, Seriola, Temnodon, Antennarius, Sternoptycliidce, Astronesthes, Exocoetus, Tetrodon, Diodon ; and only one genus of sharks, Galeocerdo, approaches the Arctic Circle. Some few species, like Antennarius, Scopelus, are carried by currents near to the farther confines of the temperate zones ; but such occurrences are accidental, and these fishes must be regarded as entirely foreign to the fauna of those latitudes. On the other hand, some pelagic fishes inhabit the temperate zones, whilst their occurrence within the tropics is very problematical ; thus, in the Atlantic, Thalassorhinus, Selache, Lwmargvs, Centrolophus, Diana, Ausonia, Lampris (all genera composed of one or two species only). Besides the shark mentioned, no other pelagic fishes are known from the Arctic Ocean. We possess very little information about the pelagic fish- fauna of the southern oceans. This much only is certain, that the tropical forms gradually disappear ; but it would be hazardous, in the present state of our knowledge, to state even approximately the limits of the southward range of a single genus. Scarcely more is known about the appearance of types peculiar to the southern temperate zone, for instance, the gigantic shark Rhinodon repre senting the northern Selache, near the coasts of South Africa, and the Scombroid genus Gastrochisma, in the South Pacific.