84 THE OLD RED SANDSTONE. 
VUI., fig. 3.) It seems a piece of exquisite shell-work, such 
as we sometimes see on the walls of a grotto. ‘There are 
two dorsals—the posterior, immediately over the tail, and 
directly opposite the anal fin; the anterior, somewhat higher 
up than the ventrals; and all the fins are of great size. The 
anterior edge of each is formed of a strong spine, round as 
the handle of a halbert, and diminishing gradually and sym- 
metrically to a sharp point. Though formed externally of 
solid bone, it seems to have been composed internally of car- 
tilage, like the bones of some of the osseous fishes — those 
of the halibut, for instance ; and the place of the cartilage is 
generally occupied in the stone by carbonate of lime. ‘The 
membrane which formed the body of the fin was covered, 
like that of the Cheiracanthus, with minute scales, of the 
same scallop-like pattern with the rest, but of not more than 
one sixth the size of those which cover the creature’s sides 
and back. Imagine two lug-sails stiffly extended between 
the deck of a brigantine and her two masts, the latter 
raking as far aft as to form an angle of sixty degrees with 
the horizon, and some idea may be formed of the dorsals 
of this singular fish. ‘They were lug-sails, formed not to be 
acted upon by the air, but to act upon the water. None of 
my specimens show the head; but, judging from analogies 
furnished by the other families of the group, I entertain little 
doubt that it will be found to be covered, not by bony plates, 
but by minute scales, diminishing, as they approach the snout, 
into mere points. In none of the specimens does any part 
of the internal skeleton survive. 
My collection contains the remains of yet another fish of 
this group, which was unfurnished with a name only a few 
months ago, but which I first discovered about five years 
since. (See Plate VIII., fig. 2.) It is now designated the 
