The seas of the Carboniferous era abounded with similar predaceous fishes, some of which must have been of enormous size. An entire specimen has never been obtained; nor, from the destructible nature of the animal framework, can we expect to meet with one. But the hard bony parts of the animals, those capable in short of preservation in mineral accumulations, are of common occurrence in the mountain limestone beds and even among the coal seams. The dorsal spines or _ichthyodorulites_, are especially conspicuous (Fig. 28). They stood up along the creature's back like masts, the fin which was attached to the hinder margin of each, representing the sail. The spine could be raised or depressed at pleasure, its movements regulating those of the fin, much as the raising or lowering of the mast in a boat influences the lug-sail that is attached to it. The general form of these spines was long, tapering, and more or less rounded. But they assumed many varieties of surface ornament. Some species were ribbed longitudinally, and had along their posterior concave side a set of little hooks somewhat like the thorns of a rose. Others seem to have been quite smooth, and of a flattened shape, with a thick-set row of sharp hooks down both of the edges, like the spine on the tail of the sting-ray of the Mediterranean. Such weapons have considerable resemblance to the barbed spear-heads of savage tribes, and it is certain they were intended to act in a similar way, as at once offensive and defensive arms. The toothed spines of the sting-rays are still used in some parts of the world to point the warrior's spear and arrow. Is there not something suggestive in the fact that these stings, after having accomplished their appointed purpose as weapons of war in the great deep, should come to be employed over again in a like capacity on the land; and that an instrument, which was designed by the Creator as a means of protecting its possessor, should be turned by man into an implement for gratifying his cupidity and satiating his revenge? Other ichthyodorulites are elegantly ornamented by long rows of tuberculed lines arranged in a zig-zag fashion, or in straight rows tapering from base to point. In all there was a blunt unornamented base, which sank into the back and served as a point of attachment for the muscles employed in raising or depressing the spine. In some specimens the outer point appears rounded and worn, the characteristic ornament being effaced for some distance--a circumstance which probably indicates that these fishes frequented the more rocky parts of the sea.[42] [Footnote 42: See Egerton, _Quart. Jour. Geol. Soc._, vol. ix. p. 281.]