The snout is formed of an elegantly curved bone (_c_) fringed along its under edge with minute thick-set teeth. On either side it is flanked by two triangular plates, which occupy the space between the intermaxillary bone (_c_) and the upper jaws (_q q_). The eye orbits seem to have been at the corners of the intermaxillary, circumscribed by the sub-orbitals (_f g h_) and the ethmoids (_b_). The massive intermaxillary bone had its posterior margin of an angular form, and into the notch thus formed there was wedged the anterior end of a long strip of plates, which expanded as they approached the occipital part of the cranium, and terminated in three irregular plates that may represent the place of the parietal and occipital bones. The space between this belt and the upper jaws was occupied by three large plates (_i k l_) which in other ganoids, as the _osteolepis_ of the Old Red Sandstone, were united into a single pre-opercular bone of considerable size. The operculum or gill cover (_m_) was relatively large, and had an elegantly curved anterior margin. The upper jaws (_q_) were comparatively small, and had a fringe of small conical teeth. The under jaws (_r r_) reached to nearly double the length of the upper, and were similarly set round with teeth. The teeth of the megalichthys, like those of the living lepidosteus, consisted of two kinds, of which the one bristled thickly along the outer edge of the jaw as sharp minute points, averaging about a line in length, while behind this outer row lay a scattered series of much larger teeth that sometimes rose nearly an inch above the jaw. The external surface of these more formidable tusks is smooth, glittering, and minutely striated with fine lines from base to point, while the root of each is farther marked by a circle of short, deep, longitudinal furrows. The internal structure displays a close ivory, which when viewed under a microscope is seen to be made up of fine tubes radiating from the outer surface to the hollow central cavity. Some of the bones in the interior of the mouth seem to have been also furnished with an apparatus of teeth. The under surface of the cranium between the arch of the under jaws consists of two oblong central plates (_t_) surrounded by a row of sixteen irregular ones, eight on each side, and terminated in front by a large lozenge-shaped scale (_u_) which fits into their angle of junction on the one side, and into the symphysis of the jaws on the other. In the osteolepis there were likewise two large plates terminating in a similar lozenge-shaped one, but without the flanking rows. In the famous Old Red holoptychius of Clashbennie, the under surface of the head had but two plates, and in the still older and more gigantic asterolepis, there was but one. It is the delightful task of the paleontologist to compare and contrast these various pieces of mechanism, to mark how what seems lacking in one comes to be supplied in another, and to