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The Polypedatidae, or glandless Tree Frogs with narrowed sacrum, are almost equally numerous in the Oriental and Neotropical regions, more than forty species inhabiting each, while in the Ethiopian there are about half this number, and the remainder are scattered over the other three regions, as shown in the enumeration of the genera — Iwalus (16 sp.), Oriental, except one in Japan, and one in Western Polynesia; Rhacophorus (7 sp.), and Theloderma (1 sp.), are Oriental; Hylarana (10 sp.), Oriental, to the Solomon Islands and Tartary, Nicobar Islands, West Africa, and Madagascar; Megalia’alus (1 sp.), Seychelle Islands; Leptomantis (1 sp.), Philippines; Platymantis (5 sp.), New Guinea, Philippines, and Fiji Islands; Cornuser (2 sp), Java and New Guinea; Polypedates (19 sp.), mostly Oriental, but two species in West Africa, one Madagascar, two Japan, one Loo-Choo Islands, and one Hong Kong; Hylambates (3 sp.), Hemimantis (1 sp.), and Chiromantis (1 sp.), are Ethiopian; Rappia (13 sp.), is Ethiopian, and extends to Madagascar and the Seychelle Islands; Acris (2 sp.), is North American; Elosia (1 sp.), Epirhizis (1 sp.), Phyllobates (9 sp.), Hylodes (26 sp.), Hylocalus (1 sp.), Pristimantis (1 sp.), Crossodactylus (1 sp.), Calostethus (1 sp.), Strabomantis (1 sp.), and Leiyla (1 sp.), are Neotropical, the last two being Central American, while species of Hylodes and Phyllobates are found in the West Indian Islands.
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The Ranidae, or true Frogs, are characterised by having simple undilated toes, but neither neck-glands nor dilated Sacrum. They are almost cosmopolitan, extending to the extreme north and south from the North Cape to Patagonia, and they are equally at home in the tropics. They are perhaps most abundant in South America, where a large number of the genera and species are found; the Ethiopian region comes next, while they are rather less abundant in the Oriental and Australian regions; the Nearctic region has much less (about 12 species), while the Palaearctic has only five, and these two northern regions only possess the single genus Rana. The genera are distributed as follows:– Rana (60 sp.), ranges all over the world, except Australia and South America, although it extends into New Guinea and into Mexico and Central America; it is most abundant in Africa. Pyoicephalus (7 sp.), extends over the whole Ethiopian region, Hindostan, the Himalayas, and Japan; Cystignathus (22 sp.), is mainly Neotropical, but has three species Ethiopian. All the other genera are confined to single regions. The Neotropical genera are:—Odontophrynus (1 sp.), Pseudis (1 sp.), Pithecopsis (1 sp.), Ensophleus (1 sp.), Limnocharis (1 sp.), Hemiphractus (1 sp.), all Tropical South American east of Andes; Ceratophrys (5 sp.), Panama to La Plata; Cycloramphus (1 sp.), West Ecuador and Chili; Pleurodema (6 sp.), Venezuela to Patagonia; Leiuperus (12 sp.), Mexico and St. Domingo to Patagonia; Hylorhina (1 sp.), Chiloe. The Australian genera are:—Mya!ophyes (1 sp.), Queensland; Platyplectrum (2 sp.), Queensland and West Australia; Neobatrachus (1 sp.), South Australia; Limnodynastes 7 sp.), and Crinia (11 sp.), Australia and Tasmania. The
Oriental genera are:–Dicroglossus (1 sp.), Western Himalayas; Oxyglossus (2 sp.), Siam to Java, Philippines and China; Hoplobatrachus (1 sp.), Ceylon; Phrynoglossus (1 sp.), Siam. The Ethiopian genera are:—Phrynobatrachus (1 sp.), Stenorhynchus (1 sp.), both from Natal.
The Discoglossidae, or Frogs with a dilated sacrum, are remarkable for the number of generic forms scattered over a large part of the globe, being only absent from the Nearctic and the northern half of the Neotropical regions, and also from Hindostan and East Africa. The genera are:— * : Chiroleptes (4 sp.), Australia; Calyplocephalus (1 sp.), allied to the preceding, from Chili; Cryptotis (1 sp.), Australia; Asterophys (2 sp.), New Guinea and Aru Islands; Xenophrys (1 sp.), Eastern Himalayas; Megalophrys (2 sp.), Ceylon and the Malay Islands; Nannophrys (1 sp.), Ceylon; Pelodytes (1 sp.), France only; Leptobrachium (1 sp.), Java; Discoglossus (1 sp.), Vienna to Algiers; Laprissa (1 sp.), Latonia (1 sp.), Palaearctic region; Arthroleptis (2 sp.), West Africa and the Cape; Grypiscus (1 sp.), South Brazil.
The Pipide are toads without a tongue or maxillary teeth, and with enormously dilated sacrum. The only species of Pipa is a native of Guiana.
The Dactylethridae are Toads with maxillary teeth but no tongue, and with enormously dilated sacrum. The species of Dactylethra are natives of West, East, and South Africa.
General Remarks on the Distribution of the Amphibia.
The Amphibia, as here enumerated, consist of 22 families, 152 genera, and nearly 700 species. Many of the families have a very limited range, only two (Ranidae and Polypedatidae) being nearly universal; five more extend each into five regions, while no less than thirteen of the families are confined to one, two, or three regions each. By far the richest region is the Neotropical, possessing 16 families (four of them peculiar) and about 50 peculiar or very characteristic genera. Next comes the Australian, with 11 families (one of which is peculiar) and 16 peculiar genera. The Nearctic region has no less than 9 of the families (two of them peculiar to it) and 15 peculiar genera, 13 of which are tailed Batrachians which have here their metropolis. The other three regions have 9 families each; the Palaearctic has no peculiar family but no less than 15 peculiar genera; the Ethiopian 1 family and 12 genera peculiar to it; and the Oriental, 19 genera but no family confined to it.
It is evident, therefore, that each of the regions is well characterised by its peculiar forms of Amphibia, there being only a few genera, such as Hyla, Rana, and Bufo which have a Wide range. The connection of the Australian and Neotropical regions is well shown in this group, by the Phryniscidae, Hylidae, and Discoglossidae, which present allied forms in both ; as well as by the genus Liopelma of New Zealand, allied to the Bombinatoridae of South America, and the absence of the otherwise cosmopolitan genus Rana from both continents. The affinity of the Nearctic and Palaearctic regions is shown by the Proteidae, which are confined to them, as well as by the genus Triton and almost the whole of the extensive family of the Salamandridae. The other regions are also well differentiated, and there is no sign of a special Ethiopian Amphibian fauna extending over the peninsula of India, or of the Oriental and Palaearctic regions merging into each other, except by means of genera of universal distribution.
Fossil Amphibia.-The extinct Iabyrinthodontia form a separate order, which existed from the Carboniferous to the Triassic period. No other remains of this class are found till we reach the Tertiary formation, when Newts and Salamanders as well as Frogs and Toads occur, most frequently in the Miocene deposits. The most remarkable is the Andrias Scheuchzeri from the Miocene of GEningen, which is allied to Sieboldia maxima the great Salamander of Japan.