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The number of species contained in this group is not great, and they have all been made known to science within a comparatively recent period. They are not of large size; their forms are slender; but they are most readily distinguished by the oar-like form of their tail, which organ, as well as the posterior part of the body, is flattened vertically, so as greatly to resemble that of an eel, and in some cases, is dilated in the same direction.

The nostrils are closed by a scale, and, as well as the eyes, are so situated as to have a vertical aspect; the pupils are circular, indicating diurnal activity; the ventral plates, formed of two united scales, are narrow, and occupy only the central line of the belly instead of its whole breadth; there are no spurs, nor any vestiges of limbs.

These Marine Snakes are highly venomous, though their teeth display a structure somewhat differing from that of the fangs of the Viperadæ. “The character,” remarks Professor Owen, “most commonly adduced from the dental system as distinguishing the venomous from the non-venomous Serpents, is, that the former have two,