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The Oligodontidæ are a small family of Ground Snakes which have been separated from the Calamariidæ, and, with the exception of a few species, are confined to the Oriental region. The best characterised genera are :
Oligodon (12 sp.), India, Ceylon, and Philippines ; and, Simotes (24 sp.), India to China and Borneo. In addition to these, Achalinus is founded on a single species from Japan; and Teleolepis consists of three species from North and South America.
FAMILY 7.-COLUBRIDÆ. (50 Genera, 270 Species.) )
The Colubrine Snakes are universally distributed over the globe, and they reach the extreme northern limits of the order. They are, however, almost absent from Australia, being there represented only by a few species of Tropidonotus and Coronella in the northern and eastern districts. This great family consists of four divisions or sub-families : the Coronellinæ (20 genera, 100 species), the Colubrinæ (16 genera, 70 species), the Dryadinæ (7 genera, 50 species), and the Natricinæ (7 genera, 50 species). The more important genera of Colubridæ are the following:
Ablabes, Coronella, Ptyas, Coluber, and Tropidonotus--all have a very wide distribution, but the two last are absent from South America, although Tropidonotus reaches Guatemala; Tomodon, Xenodon, Liopis, Stenorhina, Erythrolampus, Elapochrus, Callirhinus, Enophrys, and Dromicus—are confined to the Neotropical region; Hypsirhynchus, Cryptodacus, Jaltris, and Coloragia, are confined to the West Indian Islands; Chilomeniscus, Conophis, Pituophis, and Ischcognathus, to North America, the latter going as far south as Guatemala; Compsosoma, Zamenis, Zaocys, A tretium, Xenochrophys, and Herpetoreas, are peculiarly Oriental, but Zamenis extends into South Europe;
Lytorhynchus, Rhamnophis, Herpetethiops and Grayia, are Ethiopian; Rhinechis is peculiar to Europe ; Megablabes to Celebes, and Styporhynchus to Gilolo; Cyclophis, is found in the Oriental region, Japan, and North America ; Spilotes, in the Nearctic and Neotropical regions ; Xenelaphis in the Oriental, Ethiopian, and Palæarctic regions; Philodryas, Heterodon and Herpetodryas in America and Madagascar, the latter genus being also found in China.
FAMILY 8.--HOMALOPSIDÆ. (24 Genera, 50 Species.)
The Homalopsidæ, or Fresh-water Snakes, have been separated from the Hydridæ by Dr. Günther, and they include some groups which have been usually classed with the Natricinæ. They are especially characteristic of the Oriental region, where considerably more than half the genera and species are found; next comes the Neotropical region which has 6 species; while none of the other regions have more than 4 or 5. It is to be observed that the Ethiopian species occur in West Africa only, and mostly constitute peculiar genera, so that in this family the separation of the Ethiopian and Oriental regions is very well marked. The best characterised genera of the family are the following:
Cantoria (10 sp.), ranging from Europe to Japan, the Philippines, and Timor, with one species in Guinea ; Hypsirhina (6 sp.), Bengal, China, and Borneo; Fordonia (3 sp.), Rangoon to Borneo and Timor; Homalopsis (2 sp.), Cambodja to Java; Cerberus (2 sp.), Ceylon and Siam, the Malay Islands, New Guinea, and North Australia; Herpeton (1 sp.), Siam; Ferania (1 sp.), Bengal to Penang; Pythonopsis (1 sp.), Borneo; Myron (2 sp.), India and North Australia; Homalophis (1 sp.), Borneo; Hipistes (1 sp.), Penang; Xenodermus (1 sp.), Java; Neusterophis and Limnophis, with one species each, are peculiar to West
Africa; Helicops (2 sp.), North and South America; Farancia and Dimodes, with one species each, are from New Orleans; and a few others imperfectly known from Tropical America.
FAMILY 9.-PSAMMOPHIDÆ. (5 Genera, 20 Species.)
The Psammophidæ, or Desert Snakes, are a small group characteristic of the Ethiopian and Oriental regions, but more abundant in the former. The distribution of the genera is as follows :
Psammophis (16 sp.), ranges from West Africa to Persia and Calcutta; Calopeltis (1 sp.), North and West Africa; Mimophis (1 sp.), Madagascar; Psammodynastes (2 sp.), Sikhim to Cochin China, Borneo and the Philippine Islands; and Dromophis (1 sp.), Tropical Africa.
FAMILY 10.-RACHIODONTIDÆ. (1 Genus, 2 Species.)
The Rachiodontidae are a small and very isolated group of snakes of doubtful affinities. The only genus, Dasypeltis (2 sp.), is confined to West and South Africa.
FAMILY 11.- DENDROPAIDÆ (7 Genera, 35 Species.)
The Dendrophidæ, or Tree Snakes, are found in all the Tropical regions, but are most abundant in the Oriental. The genera are distributed as follows
Dendrophis ranges from India and Ceylon to the Pelew Islands and North Australia, and has one species in West Africa; Ahætulla is almost equally divided between Tropical Africa and Tropical America; Gonyosoma ranges from Persia to Java and the Philippines ; Chrysopelea is found in India, Borneo, the Philippines, Amboyna, and Mysol ; Hapsidrophis and Bucephalus are confined to Tropical Africa ; and Ithycyphus (1 sp.), is peculiar to Madagascar.
FAMILY 12.-DRYIOPHIDÆ. (5 Genera, 15 Species.)
The Dryiophidæ, or Whip Snakes, are a very well characterised family of slender, green-coloured, arboreal serpents, found in the three tropical regions but absent from Australia, although they just enter the Australian region in the island of Celebes. In Africa they are confined to the West Coast and Madagascar. The genera are :
Dryiophis (4.sp.), Tropical America and West Africa : Tropidococcyx (1 sp.), Central India; Tragops (4 sp.), Bengal to China, the Philippines, Java, and Celebes ; Passerita (2 sp.), Ceylon
and the Indian Peninsula ; and Langaha (2 sp.), confined to Madagascar.
FAMILY 13.—DIPSADIDÆ. (11 Genera, 45 Species.)
The Dipsadidæ, or Nocturnal Tree Snakes, are distinguished from the last family by their dark colours and nocturnal habits. They are about equally abundant in the Oriental and Neotropical regions, less so in the Ethiopian, while only a single species extends to North Australia. The following are the best known genera :
Dipsas, comprising all the Oriental species with one in AsiaMinor, and a few from the Moluccas, New Guinea, North Australia, West Africa, and Tropical America; Thamnodyastes, Tropidodipsas, and several others, from Tropical America; Dipsadoboa, from West Africa and Tropical America; Leptodeira, from Tropical and South Africa, South America, and Mexico; and Pythonodipsas, from Central Africa.
FAMILY 14.—SCYTALIDÆ. (3 Genera, 10 Species.)
It is doubtful how far the three genera which constitute this family form a natural assemblage. We can therefore draw no safe conclusions from the peculiarity of their distributionScytale and Oxyrhopus being confined to Tropical America; while Hologerrhum inhabits the Philippine Islands.