forsteri_ of the Australian seas. The Pilot Whale (_Globicephalus melas_) and the _Pseudorca_ of the North Atlantic and of New Zealand are also, so far as present knowledge enables us to judge, respectively alike. Many other similar cases might be given. Captain Maury collected much valuable evidence about the distribution of the larger Cetacea, and, finding Right Whales (_Balæna_) common in both northern and southern temperate seas, and absent in the intermediate region, laid down the axiom that “the torrid zone is to the Right Whale as a sea of fire, through which he cannot pass.” Hence all cetologists have assumed that the Right Whale of the North Atlantic (_B. biscayensis_), that of the South Seas (_B. australis_), and that of the North Pacific (_B. japonica_), are necessarily distinct species. The anatomical structure and external appearance of all are, however, so far as yet known, marvellously alike, and, unless some distinguishing characters can be pointed out, it seems scarcely justifiable to separate them from geographical position alone; as, though the tropical seas may be usually avoided by them, it does not seem impossible, or even improbable, that some individuals of animals of such size and rapid powers of swimming may have at some time traversed so small a space of ocean as that which divides the present habitual localities of these supposed distinct species. If identity or diversity of structural characters is not to be allowed as a test of species in these cases, as it is usually admitted to be in others, the study of their geographical distribution becomes an impossibility. Although many species are thus apparently of such wide distribution, others are certainly restricted; thus the Arctic Right Whale (_Balæna mysticetus_) has been conclusively shown to be limited in its range to the region of the northern circumpolar ice, and no corresponding species has been met with in the southern hemisphere. In this case, not only temperature, but also the peculiarity of its mode of feeding, may be the cause. The Narwhal and the Beluga have a very similar distribution, though the latter occasionally ranges farther south. The common Hyperoödon is restricted to the North Atlantic, never entering, so far as is yet known, the tropical seas. Other species are exclusively tropical or austral in their range. One of the true Whalebone Whales (_Neobalæna marginata_) has only been met with hitherto in the seas round Australia and New Zealand; and a large Ziphioid (_Berardius arnouxi_) only near the last-named islands.