442 RAMBLES OF A GEOLOGIST. 



portions of the organism ; for the thinner parts, too incon- 

 siderable to have served as attractive nuclei to the stony mai>- 

 ter when the concretion was forming, were left outside its 

 pale, and so have been lost; whereas, in the northern dis- 

 tricts of the deposit, where the fossils, as in Caithness and 

 Orkney, occur in flagstone, these slimmer parts, when the 

 general state of keeping is tolerably good, lie spread out on 

 the planes of the slabs, entire often in their minutest rays 

 and articulations. The numerous Coccostei of this quarry 

 exhibit, attached to their upper plates, their long vertebral 

 columns, of many joints, that, depending from the broad dor- 

 sal shields of the ichthyolite, remind one of those skeleton 

 fishes one sometimes sees on the shores of a fishing village, in 

 which the bared backbone joints on, cord-like, to the broad 

 plates of the skull. None of the other fishes of the Old Red 

 Sandstone possessed an internal skeleton so decidedly osseous 

 as that of the Coccosteus, and none of them presented ex- 

 ternally so large an extent of naked skin, provisions which 

 probably went together. For about three-fifths of the entire 

 length of the animal the surface was unprotected by dermal 

 plates; and the muscles must have found the fulcrums on 

 which they acted in the internal skeleton exclusively. And 

 hence a necessity for greater strength in their interior frame- 

 work than in that of fishes as strongly fenced round exter- 

 nally by scales or plates as the coleoptera by their ely trine, 

 or the Crustacea by their shells. Even in the Coccosteus, 

 however, the ossification was by no means complete ; and the 

 analogies of the skeleton seem to have allied it rather with 

 the skeletons of the sturgeon family than with the skele- 

 tons of the sharks or rays. The processes of the vertebrae 

 were greatly more solid in their substance than the vertebrae 

 themselves, a condition which in the sharks and rays is 

 always reversed ; and they frequently survive, each with its 

 little sprig of bone, formed like the letter Y, that attached 



