78 THE OLD RED SANDSTONE. 
found to present somewhat the appearance of the outer side 
of the deep-sea cockle, with its strongly marked ribs and chan- 
nels, the point in which the posterior point terminates repre- 
senting the hinge. (See Plate VI., fig. 2.) The bones of 
the head, enamelled like the scales, are carved into jagged 
inequalities, somewhat resembling those on the skin of the 
shark, but more irregular. The sculpturings seem intended 
‘evidently for effect. To produce harmony of appearance 
between the scaly coat and the enamelled occipital plates of 
bone, the surfaces of the latter are relieved, where they border 
on the shoulders, into what seem scales, just as the dead 
walls of a building are sometimes, for the sake of uniformity, 
wrought into blind windows. ‘The enamelled rays of the fins 
are finished, if I may so speak, after the same style. They 
lie thick upon one another as the fibres of a quill, and like 
these, too, they are imbricated on the sides, so that the edge 
of each seems jagged into a rowof prickles. (See Plate VI., 
fig. 3.) The jaws of the Cheirolepis were armed with thickly- 
set sharp teeth, like those of its contemporaries, the Osteolepis 
and Diplopterus.* 
* There have been five species of Cheirolepis enumerated — C. 
Cummingie, C. splendens, C. Traillii, C. unilateralis, and C. Uragus. 
The Chetrolepis splendens and C. wumnilateralis Agassiz regards as 
doubtful. 
