Scattered over the fresh-water limestones, ironstones, and shales, or crowded together along the upper surface of some of the coal-seams, there occur the remains of two very remarkable ganoidal fishes. They deserve our attention for their great size, their complex organization, and the important place in the scale of animal life which they occupied during a former period. One of them has been called _megalichthys_ or _great fish_--an unhappy name, since the animal did not reach the dimensions attained by not a few of the other ganoids, and was even surpassed by at least one of its contemporary congeners. The other is known as the _holoptychius_ or _wrinkled scale_. A more detailed examination of these two animals will perhaps best enable us to understand the character of the ganoid fishes that lived in the waters of the Carboniferous period. The megalichthys had an average length of about three feet. Like the other members of the ganoid order it had a glittering exterior, every scale and plate being formed of strong bone, and coated with a bright layer of enamel. Wherever this polished surface extends, it is found to be ornamented with a minute punctulation, the pores of which lie thickly together like the finer dots of a stippled engraving. The cranial plates are further varied by a scattered and irregular series of larger punctures that look as if they had been formed by the insertion of a pin-point into a soft yielding surface. The examination of the head of the megalichthys as depicted in Fig. 30, will convey an adequate conception of the structure of a ganoidal cranium. [Illustration: Fig. 30.--Head of Megalichthys Hibberti, one-sixth of natural size (Agass. _Poiss. Foss._ Tab. 63). A Upper side. B. Under side. C Profile.]