The seas of the period contained a great number of the fishes called _Ganoids_; which are so called from the splendour of the hard and enamelled scales, which formed a sort of defensive armour to protect their bodies. _Lepidotus gigas_ was a fish of great size belonging to this age. A smaller fish was the _Tetragonolepis_, or _Æchmodus Buchii_. The _Acrodus nobilis_, of which the teeth are still preserved, and popularly known by the name of _fossil leeches_, was a fish of which an entire skeleton has never been met with. Neither are we better informed as to the _Hybodus reticulatus_. The bony spines, which form the anterior part of the dorsal fin of this fish, had long been an object of curiosity to geologists, under the general name of _Ichthyodorulites_, before they were known to be fragments of the fin of the _Hybodus_. The Ichthyodorulites were supposed by some naturalists to be the jaw of some animal--by others, weapons like those of the living _Balistes_ or _Silurus_; but Agassiz has shown them to be neither the one nor the other, but bony spines on the fin, like those of the living genera of _Cestracions_ and _Chimæras_, in both of which the concave face is armed with small spines like those of the _Hybodus_. The spines were simply imbedded in the flesh, and attached to it by strong muscles. “They served,” says Dr. Buckland, “as in the _Chimæra_, to raise and depress the fin, their action resembling that of a movable mast lowering backward.” [Illustration: Fig. 94.--Ichthyosaurus communis.] Let us hasten to say, however, that these are not the beings that characterised the age, and were the salient features of the generation of animals which existed during the Jurassic period. These distinguishing features are found in the enormous reptiles with lizard’s head, crocodile’s conical teeth, the trunk and tail of a quadruped, whale-like paddles, and the double-concave vertebræ of fishes; and this strange form, on such a gigantic scale that even their inanimate remains are examined with a curiosity not unmixed with awe. The country round Lyme Regis, in Dorsetshire, has long been celebrated for the curious fossils discovered in its quarries, and preserved in the muddy accumulations of the sea of the Liassic period. The country is hilly--“up one hill and down another,” is a pretty correct provincial description of the walk from Bridport to Lyme Regis--where some of the most frightful creatures the living world has probably ever beheld, sleep the sleep of stones. The quarries of Lyme Regis form the cemetery of the Ichthyosauri; the sepulchre where lie interred these dragons of the ancient seas.