156 THE OLD RED SANDSTONE. 
peculiarities of the Holoptychius, that they strike the com- 
monest observer. 
The scales are very characteristic. ‘They are massy ellipti- 
cal plates, scarcely less bulky in proportion to their extent of 
surface than our smaller copper coin, composed internally of 
bone, and externally of enamel, and presenting on the one 
side a porous structure, and on the other, when well pre- 
served, a bright, glossy surface. ‘The upper, or glossy side, 
is the more characteristic of the two. I have placed one of 
them before me. Imagine an elliptical ivory counter, an inch 
and a half in length by an inch in breadth, and nearly an 
eighth part of an inch in thickness, the larger diameter 
forming a line which, if extended, would pass longitudinally 
from head to tail through the animal which the scale covered. 
On the upper or anterior margin of this elliptical counter, 
imagine a smooth selvedge or border three eighth parts of an 
inch in breadth. Beneath this border there is an inner border 
of detached tubercles, and beneath the tubercles large undu- 
lating furrows, which stretch longitudinally towards the lower 
end of the ellipsis. Some of these waved furrows run un- 
broken and separate to the bottom, some merge into their 
neighboring furrows at acute angles, some branch out and 
again unite, like streams which enclose islands, and some 
break into chains of detached tubercles. (See Plate XII, fig. 3.) 
No two scales exactly resemble one another in the minuter 
peculiarities of their sculpture, if I may so speak, just as no 
two pieces of lake or sea may be roughened after exactly 
the same pattern during a gale; and yet in general appear- 
ance they are all wonderfully alike. Their style of sculpture 
is the same —a style which has sometimes reminded me of 
the Runic knots of our ancient north country obelisks. Such 
was the scale of the creature.* The head, which was small, 
* See Note L. 
