The internal bones of the holoptychius were of great size and strength, as befitted such a bulky ganoid. Some of them had a singular style of surface ornament, that somewhat resembled a frosted widow on a December morning. Their internal structure was loose and cancellated; the endo- being usually of a less compact texture than the exo-skeleton. Judging from the size of such bones, the carboniferous holoptychius must have been one of the bulkiest and most formidable denizens of the deep, reaching sometimes to a length of twenty feet or even more. Such an animal would have been, perhaps, quite a match for our hugest crocodile or alligator, for it must have swum about with a litheness and agility possessed by none of the saurian reptiles. Like that leviathan chosen by the Almighty, in an age long subsequent, as an illustration of His power and greatness, the holoptychius must have been king over all the inhabitants of the sea, and the magnificent language of Job, descriptive of the living animal, applies not less graphically to the extinct one: "Who can open the doors of his face? his teeth are terrible round about. His scales are his pride, shut up together as with a close seal. One is so near to another, that no air can come between them. He maketh the deep to boil like a pot: he maketh the sea like a pot of ointment. He maketh a path to shine after him; one would think the deep to be hoary." Our survey has hitherto been directed to the denizens of carboniferous lake, river, and sea, and we have found them to be alike important in numbers and interesting in organization. It is otherwise, however, when we turn in search of the denizens of the carboniferous lands. The crowded trees and shrubs of the coal strata recalling as they do old forest-covered swamps, might seem to indicate the probability of a pretty numerous terrestrial fauna. Where are we to look for the fossilized relics of land animals, if not in the remains of a submerged land-surface? And yet, strange as it may seem, of the inhabitants of the land during the Coal-measure period we know almost nothing. "We have ransacked hundreds of soils replete with the fossil roots of trees,--have dug out hundreds of erect trunks and stumps, which stood in the position in which they grew,--have broken up myriads of cubic feet of fuel, still retaining its vegetable structure,--and, after all, we continue almost as much in the dark regarding the invertebrate air-breathers of this epoch, as if the coal had been thrown down in mid-ocean."[50] [Footnote 50: Sir Charles Lyell's _Elements_, fifth edition, p. 406.]