The larger snakes of this family are all highly dangerous to man ; the venom is chiefly neurotoxic in its action, as compared with the more haemolytic venom of the back-fanged Colubrids and Vipers.
9. Hydrophiidae.—Sea-snakes. Elapids adapted to aquatic life, with valvular nostrils on the top of the snout, vertically flattened tails and the ventral shields greatly reduced or entirely absent ; all produce their young fully developed. The snakes of this family, some 55 all told, are divided into two sub-families, the one (Laticaudinae) Australian in origin, the other (Hydrophiidae) Indo-Malayan ; they are found throughout the tropical waters of the Indian and Pacific Oceans, but not in the Atlantic, and, though many are admirably adapted for aquatic life, and indeed are quite helpless on land, they chiefly frequent inshore waters and are most numerous around the coasts of the Indian region and along the chain of islands to north Australia; all are veno mous, though the majority are very docile. The majority do not exceed four feet in length but a few reach a length of eight feet or more and many are of great girth, the greatest diameter being in the posterior half of the body, which gradually tapers towards the head ; colours, as a rule, are indistinct transverse bands of darker and lighter but the most widely distributed species Pelamis platurus, which ranges from the east coast of Africa to the west coast of America, is uniformly black above and yellowish or brown beneath, the two colours being sharply defined in a straight line along the sides but forming vertical bars or spots on the tail.
1o. Viperidae.—Vipers and rattlesnakes are characterized by the possession of poison fangs situated on the front of an upper jaw which is movable so that the teeth, when not in use, can be folded down parallel with the roof of the mouth ; cosmopolitan except the Australian region and Madagascar. As a rule the members of this family are stoutly built, with flattened heads which lack the large plates so characteristic of the majority of the other poison ous snakes. For furthr details see VIPERS. (H. W. P.)