which are very distinct from all that follow, though less so from certain of the harmless species appertaining to the two families last treated of. Some of their distinctions have been already noticed (p. 45), but they are especially characterised by their highly compressed tail, indicative of their thoroughly aquatic habits. According to Dr. Günther, there is no other group of Reptiles the species of which are so little known, and the synonymy of which is so much confused, as that of the Sea Snakes. Most naturalists who have worked at them have been misled by the idea that the species were not nearly so numerous as they actually are. Mr. W. Theobald makes out as many as twenty-five inhabiting the Bay of Bengal and the adjacent seas, to which area this group of Reptiles is mainly confined, a few species extending to northern Australia, and one, the most emphatically pelagic, the _Pelamis bicolor_, even to the Pacific Ocean. One genus only, _Platurus_, approaches the Land Snakes in several of its characters; having much the physiognomy of an _Elaps_, with the cleft of the mouth not turned upwards behind, as in other Sea Snakes; the eye also is rather small, nor is the tail at all prehensile. There are two species of this particular form, one of which, _P. scutatus_, is rather common, and its geographic range extends from the Bay of Bengal and the China seas to the coasts of New Zealand; the distribution of the other, _P. Fischeri_, being nearly as extensive. The great genus _Hydrophis_ has the posterior part of the body highly compressed, and most of the species are more or less of a bluish lead-colour, like that of the sea, or black, banded with white or yellowish white. They are so abundant in the Indian seas that some of them are taken with every haul of a fishing-net, and they are helpless and seemingly blind when out of the water; the fishermen commonly seizing them, one after the other, by the nape and throwing them back into the sea. Some of them (_Microcephalophis_ of Lesson) have the head very small and the neck exceedingly slender, while the compressed body is large and thick. THE COLUBRINE Venemous SNAKES.