Mr. Conybeare was enabled, in 1824, after examining many skeletons nearly perfect, to give an ideal restoration of the osteology of this genus, and of that of the _ Plesiosaurus._[5] (See Figs. 380, 381.) The latter animal had an extremely long neck and small head, with teeth like those of the crocodile, and paddles analogous to those of the _ Ichthyosaurus,_ but larger. It is supposed to have lived in shallow seas and estuaries, and to have breathed air like the Ichthyosaur and our modern cetacea.[6] Some of the reptiles above mentioned were of formidable dimensions. One specimen of _ Ichthyosaurus platydon,_ from the Lias at Lyme, now in the British Museum, must have belonged to an animal more than 24 feet in length; and there are species of _Plesiosaurus_ which measure from 18 to 20 feet in length. The form of the _ Ichthyosaurus_ may have fitted it to cut through the waves like the porpoise; as it was furnished besides its paddles with a tail-fin so constructed as to be a powerful organ of motion; but it is supposed that the _Plesiosaurus,_ at least the long-necked species (Fig. 381), was better suited to fish in shallow creeks and bays defended from heavy breakers. It is now very generally agreed that these extinct saurians must have inhabited the sea; and it was urged that as there are now chelonians, like the tortoise, living in fresh water, and others, as the turtle, frequenting the ocean, so there may have been formerly some saurians proper to salt, others to fresh water. The common crocodile of the Ganges is well-known to frequent equally that river and the brackish and salt water near its mouth; and crocodiles are said in like manner to be abundant both in the rivers of the Isla de Pinos (Isle of Pines), south of Cuba, and in the open sea round the coast. In 1835 a curious lizard (_Amblyrhynchus cristatus_) was discovered by Mr. Darwin in the Galapagos Islands.[7] It was found to be exclusively marine, swimming easily by means of its flattened tail, and subsisting chiefly on seaweed. One of them was sunk from the ship by a heavy weight, and on being drawn up after an hour was quite unharmed. Fig. 380: Skeleton of Ichthyosaurus communis, restored by Conybeare and Cuvier. Fig. 381: Skeleton of Plesiosaurus dolichodeirus, restored by Rev. W. D. Conybeare. The families of Dinosauria, crocodiles, and Pterosauria or winged reptiles, are also represented in the Lias. Sudden Destruction of Saurians.—It has been remarked, and truly, that many of the fish and saurians, found fossil in the Lias, must have met with sudden death and immediate burial; and that the destructive operation, whatever may have been its nature, was often repeated.