OCR Text |
Show 1897.] DISTRIBUTION OF MARINE MAMMALS. 357 Seals, appears to have been originally an Antarctic group, and the greater number of its species, although now-a-days very much reduced in numbers, are still found in the Southern Ocean. But the Otarice have travelled still further north than Macrorhinus, and three, if not four, species are, as already stated, in these clays well established inhabitants of Arctirenia. The Sirenians are absent from Notopelagia, but Cetaceans of every kind are abundant. Besides one or more representatives of the true Whalebone Whale (Balcena), Notopelagia has a smaller representative of the group (Neohalcena) entirely restricted to its area. It has also representatives of Megaptera and Balcenoptera, though it is doubtful how far they are even specifically distinct from some of their northern representatives. Among the Toothed Whales (Odontoceti) we find a large Ziphioid form, Berardlus, restricted to the Notopelagian area, while Ziphius and Mesoplodon also occur there. The Dolphins (Delphlnldce) are likewise numerous, and present some distinct species, but not, so far as our present knowledge extends, any generic forms that do not occur elsewhere. But Notopelagia is sufficiently distinguished from all tbe five more northern sea-regions by possessing four genera of Seals and two of Cetaceans entirely restricted to its area. XII. Conclusions. It has therefore, I think, been shown that, for the Geography of Marine Mammals, the Ocean may be conveniently divided into six Sea-regions, which, as marked in the chart now exhibited (Plate XXIV.), are as follows :- I. REGIO ARCTATLANTICA, characterized by its Seals (Phoclnce), of wdiich two genera, Halichcerus and Cystophora, are peculiar, whilst Phcca is common to it and Arctirenia; by the absence of Sirenians; and by the possession of three peculiar genera of Cetaceans (Hyperoodon, Delphlnapterus, and Monodon). II. R E G I O MESATLANTICA, sole possessor of the Monk-Seal, Monachus, amongst the Pinnipeds, and of the Sirenian genus Manatus. III. R E G I O INDOPELAGICA, characterized by the presence of the Sirenian Halicore and by the absence of Pinnipeds. IV. R E G I O ARCTIRENICA, wdth Phoca like the Regio Arctatlantica, but having Otaria also ; the home of the (now extinct) Sirenian Rhytlna and of the endemic Cetacean Rhachianectes. V. R E G I O MESIRENICA, without true Seals (Phoclnce), but having Otaria and Macrorhinus from the south; no Sirenian known. VI. R E G I O NOTOPELAGTCA, characterized bv four endemic genera of Phocldce, and by the presence of many Otarice ; without Sirenians, but wdth two endemic forms of Cetaceans (Neohalcena and Berardlus). |