and the membrane the sail; and it is a curious characteristic of the order, that the membrane, like the body, of the ichthyolite, is thickly covered with minute scales. The mouth seems to have opened a very little under the snout, as in the haddock; and there are no indications of its having been furnished with teeth.[X] [Footnote X: There have been three species of _Cheiracanthus_ determined--_C. microlepidotus_, _C. minor_, and _C. Murchisoni_.] [Illustration: _PLATE VII._] An ichthyolite first discovered by the writer about three years ago, and introduced by him to the notice of Agassiz during his recent visit to Edinburgh, but still unfurnished with a name,[Y] is a still more striking representative of this order than even the _Cheiracanthus_. It must have been proportionally thick and short, like some of the tropical fishes, though rather handsome than otherwise. (See Plate VIII., fig. 1.) The scales, minute, but considerably larger than those of the _Cheiracanthus_, are of a rhomboidal form, and so regularly striated--the striæ converging to a point at the posterior termination of each scale--that, when examined with a glass, the body appears as if covered with scallops. (See Plate VIII., 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 symmetrically to a sharp point. Though formed externally of solid bone, it seems to have been composed internally of cartilage, 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. [Footnote Y: Now determined to be a species of _Diplacanthus_--_D. longispinus_.] [Illustration: _PLATE VIII._]