The living Ichthyosaurus must have borne a resemblance to a Grampus or Porpoise, with four large flippers or paddles and a long tail, having a vertical caudal fin of moderate dimensions; the skin probably being naked and smooth, as in the Cetaceans. The Plesiosaurus presented a configuration still more extraordinary (Wond. p. 575). With a very small head, it possessed a neck of enormous length, a body of moderate size, with four paddles, resembling those of turtles, and a very short tail. They were both marine, air-breathing, cold-blooded, carnivorous, vertebrate animals; swarming in prodigious numbers during the secondary epochs, and particularly in the seas of the Liassic period (Ly. p. 277, figs. 310, 311). In both genera the construction of the skeleton presents many important variations from all known recent types; and should be carefully investigated by the student, who will find in the Reports of Professor Owen above referred to all the information that can be desired.[591]
[591] The Penny Cyclopædia, Art. Plesiosaurus, contains an able abstract of these Reports; and in the Fossils of the British Museum, the student will find a full account of the discovery of the Ichthyosaur and Plesiosaur, and of the deposits in which they are chiefly found, as well as detailed descriptions of the most characteristic structures of the different species.
It will suffice for our present purpose to point out a few important and obvious characters.
Lign. 209. Eye of Ichthyosaurus. 1/6 nat. Lias. Lyme Regis.
Portion of the facial part of the skull of an Ichthyosaurus, showing the position of the nostril, and of the orbit with its circle of bony plates, forming the sclerotic coat of the eye.
n. The left nasal aperture.
Lign. 210. Teeth of Ichthyosaurus and Plesiosaurus, nat.
Lias. Somersetshire.