unmuscular bag, filled with delicate viscera; but not even the human animal is more skilful in clothing himself in the spoils of other animals than the hermit crab in wrapping up its naked bag in the strong shell of some dead fusus or buccinum, which it carries about with it in all its peregrinations, as at once clothes, armor, and house. Nature arms its front, and it is itself wise enough to arm its rear. Now, it seems not improbable that the half-armed Coccosteus, a heavy fish, indifferently furnished with fins, may have burrowed, like the recent _Silurus glanis_ or _Pimelodus gulio_, in a thick mud,--of the existence of which in vast quantity, during the times of the Old Red Sandstone, the dark Caithness flagstones, the fetid breccia of Strathpeffer, and the gray stratified clays of Cromarty, Moray, and Banff, unequivocally testify; and that it may have thus not only succeeded in capturing many of its light-winged contemporaries, which it would have vainly pursued in open sea, but may have been enabled also to present to its enemies, when assailed in turn, only its armed portions, and to protect its unarmed parts in its burrow. It is further worthy of notice, that many of the Pimelodi are furnished with spines, not, like those ichthyodorulites which occur so frequently in the older Secondary and Palaeozoic divisions, unfinished in appearance at their lower extremity, as if, like the spines of the ancient Acanthodi, or those of the recent dog-fish (_Spinax acanthias_), they had been simply embedded in the flesh, but bearing, like the wings of the Pterichthys, an articulated aspect. Those of the _Pimelodus rita_ and _Pimelodus gagata_ are of singular beauty; and when the creatures have no further use for them, and the mud of the Ganges has been consolidated into shale or baked into flagstone around them, they will make very exquisite fossils. A correct drawing of the plates and spines of some of the members of the Pimelodi family, with a portion of the internal skeletons, arranged in their proper places, but divested of those more destructible parts to which they are attached, would serve admirably to show what strange forms fish not greatly removed from the ordinary type may assume in the fossil state, and might throw some light on the extraordinary appearance assumed, as ichthyolites, by the old family of the Cephalaspians.