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226 the latter have four rows of teeth in the upper jaw; the two outer, or maxillary rows being wanting in the venomous species, and their place being supplied by the single poison-fang. The exceptions to this rule, however, are too numerous for its value as a distinguishing character, in a question of such practical moment as the venomous or non-venomous properties of a Serpent. In all the family of the Marine Serpents, the poison-fang is only the foremost of a row of fixed maxillary teeth. In the Hydrophis striatus there are four teeth, and in Hydrophis schistosa five teeth behind the venom-fang, of rather smaller size than it: the two coloured Sea-Snake (Pelamys bicolor) has also five maxillary teeth, in addition to the perforated one. The poison-fang in this genus is relatively smaller than in the venomous Serpents of the land, but presents the same peculiar structure. It is a curious fact that the smaller non-venomous teeth of the poisonous Serpents all present a trace of the structure of the functional venom-fang, being more or less deeply grooved along the convex interior side; and in the Hydrus, this groove commences by a depression analogous to the oblique basal aperture of the poison-canal in the true fang.”

The prevailing colour in this Family is yellowish, often varying towards green, blue, or white, and often relieved by blackish rings, or by broad lozenge-shaped spots placed transversely across the upper parts.

The Hydrophidæ are natives of the Indian Seas, and the coasts of Australia, but some occasionally stray as far as the shores of New