similar plan;--they also are made to consist of two _coats_; and what is technically termed the _tear_ of the upper is so disposed that it lies at an angle of forty-five degrees with the _tear_ of the coat which lies underneath. Now, the inner table of the scale of the Holoptychius was composed, on this principle, of various layers or coats, arranged the one over the other, so that the fibres of each lay at right angles with the fibres of the others in immediate contact with it. In the inner table of one scale I reckon nine of these alternating, variously-disposed layers; so that any application of violence, which, in the language of the lath-splitter, would _run lengthwise along the grain_ of four of them, would be checked by the _cross grain_ in five. In other words, the line of the _tear_ in five of the layers was ranged at right angles with the line of the _tear_ in four. There were thus in a single scale, in order to secure the greatest possible amount of strength,--and who can say what other purposes may have been secured besides?--three distinct principles embodied,--the principle of the two tables and _diploe_ of the human skull,--the principle of the variously arranged coats of the human stomach,--and the principle of Oliver Cromwell's "fluted pot." There have been elaborate treatises written on those ornate flooring-tiles of the classical and middle ages, that are occasionally dug up by the antiquary amid monastic ruins, or on the sites of old Roman stations. But did any of them ever tell a story half so instructive or so strange as that told by the incalculably more ancient ganoid _tiles_ of the Palaeozoic and Secondary periods?