Although chiefly arboreal, many of the iguanas take readily to the water; and there is at least one species, _Amblyrhynchus cristatus_, which leads for the most part an aquatic life. These marine lizards occur only in the Galapagos Islands, where they are never seen more than 20 yds. inland, while they may often be observed in companies several hundreds of yards from the shore, swimming with great facility by means of their flattened tails. Their feet are all more or less webbed, but in swimming they are said to keep these organs motionless by their sides. Their food consists of marine vegetation, to obtain which they dive beneath the water, where they are able to remain, without coming to the surface to breathe, for a very considerable time. Though they are thus the most aquatic of lizards, Darwin, who studied their habits during his visit to those islands, states that when frightened they will not enter the water. Driven along a narrow ledge of rock to the edge of the sea, they preferred capture to escape by swimming, while if thrown into the water they immediately returned to the point from which they started. A land species belonging to the allied genus _Conolophus_ also occurs in the Galapagos, which differs from most of its kind in forming burrows in the ground. IGUANODON, a large extinct herbivorous land reptile from the Wealden formation of western Europe, almost completely known by numerous skeletons from Bernissart, near Mons, Belgium. It is a typical representative of the ornithopodous (Gr. for bird-footed) Dinosauria. The head is large and laterally compressed with a blunt snout, nearly terminal nostrils and relatively small eyes. The sides of the jaws are provided with a close series of grinding teeth, which are often worn down to stumps; the front of the jaws forms a toothless beak, which would be encased originally in a horny sheath. When unworn the teeth are spatulate and crimped or serrated round the edge, closely resembling those of the existing Central American lizard, _Iguana_--hence the name _Iguanodon_ (Gr. Iguana-tooth) proposed by Mantell, the discoverer of this reptile, in 1825. The bodies of the vertebrae are solid; and they are convexo-concave (i.e. _opisthocoelous_) in the neck and anterior part of the back, where there must have been much freedom of motion. The hindquarters are comparatively large and heavy, while the tail is long, deep and more or less laterally compressed, evidently adapted for swimming. The small and mobile fore-limbs bear four complete fingers, with the thumb reduced to a bony spur. The pelvis and hind-limbs much resemble those of a running bird, such as those of an emu or the extinct moa; but the basal bones (metatarsals) of the three-toed foot remain separate throughout life, thus differing from those of the running birds, which are firmly fused together even in the young adult. No external armour has been found. The reptile doubtless frequented