A tooth from the Fife coal-field, drawn for one of the woodcuts in a popular elementary manual, was also named megalichthys; an error perpetuated through every edition till the last, where the tooth has been restored to its true owner--the holoptychius. In truth, no two organisms have ever been so maltreated; and if the reader will kindly bear with me a little further, it will not be difficult to show him that the holoptychius had peculiarities of its own quite as distinct as those that have come before us in the megalichthys, and that each animal has a full and legitimate claim to a separate and independent niche in the gallery of fossil fishes. [Footnote 45: See Agassiz, _Poiss. Foss._, tom. ii. Part 2, p. 89 _et seq._] The word _holoptychius_ means, as I have said, "wrinkled or folded all over,"--a name truly expressive of the peculiar style of ornament displayed by every part of the exterior of the animal's body. The head-plates, which are of great size, exhibit a fine corrugated shagreen-like surface, roughened into knobs, and wavy lines of confluent tubercules, that remind one disposed to be fanciful, of a frosty December moon with its isolated peaks, and confluent mountain chains. The scales are of a rounded or oval form, and vary from less than half an inch to fully four or even five inches in diameter. Their upper side consists of two parts, one of which with a crescent shape lay beneath, the over-lapping scales, while the other passed outwards to form a portion of the outer visible surface. The part that was hidden by the overlapping scale was smooth, with a finely striated surface. The exposed portion displayed the usual corrugated sculpturing, many of the little tubercules having striated sides, and showing, in consequence, no little resemblance to the star-like knobs on the dermal covering of the Old Red Sandstone asterolepis. The inner surface of the scales was concave, with a central prominent oblong point surrounded by encircling scaly ridges, and forming what is called the centre of ossification.[46]