Pelagic fishes, like shore fishes, are most numerous in the Tropical Zone; and, with few exceptions (_Echinorhinus_, _Psenes_, _Sternoptychidæ_, _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 scarcer with the increasing distance from the equator. North of 40° lat. N. many genera have disappeared, or are met with in isolated examples only, as _Carcharias_, _Zygæna_, _Notidanus_, _Myliobatidæ_, _Dactylopterus_, _Echeneis_, _Nomeus_, _Coryphæna_, _Schedophilus_, _Seriola_, _Temnodon_, _Antennarius_, _Sternoptychidæ_, _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 northern 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_, _Læmargus_, _Centrolophus_, _Diana_, _Ausonia_, _Lampris_ (all genera composed of one or two species only). Beside 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. So 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_), representing the Northern Selache, near the coasts of South Africa, and the Scombroid genus, _Gastrochisma_, in the South Pacific.