afraid to communicate it,-" Do not be deterred, if you have examined minutely, by any dread of being deemed extravagant. The possibilities of existence run so deeply into the extravagant, that there is scarcely any conception too extraordinary for nature to realize." In all the more complete specimens which I have yet seen, the position of the jaws is vertical, not horizontal; and yet the creature, as shown by the tail, belonged unquestionably to the vertebrata.

Now, though the mouths of the crustaceous animals, such as the crab and lobster, open vertically, and a similar arrangement obtains among the insect tribes, it has been remarked by naturalists as an invariable condition of that higher order of animals distinguished by vertebrated columns, that their mouths. open horizontally. What I would remark as very extraordinary in the Coccosteus,-not, however, in the way of directly asserting the fact, but merely by way of soliciting inquiry regarding it,-is, that it seems to unite to a vertebral column a vertical mouth, thus forming a connecting link between two orders of existences, by conjoining what is at once their most characteristic and most dissimilar traits.

I am acquainted with four species of Coccosteus,C. latus, C. cuspidatus, C. oblongus, and a variety not yet named; and many more species may yet be discovered. Of all the existences of the formation, this curious fish seems to have been one of the most abundant. In a few square yards of rock I have laid open portions of the remains of a dozen different individuals belonging to two of the four species, the C. latus and C. cuspidatus, in the course of a single

evening. None of the other kinds have yet been found at Cromarty. These two differed from each other in the proportions which their general bulk bore to their length,-slightly too in the arrangement of their occipital plates. The Coccosteus latus, as the name implies, must have been by much a massier fish than the other; and we find the arch-like form of the plates which covered its head more complete : the plate representing the key-stone rests on the saddle-shaped plate in the centre, and the plates representing the spring-stones of the arch exhibit a broader base. The accompanying print (Plate III.) represents the Coccosteus cuspidatus. The average length of the creature, including the tail, as shown in most of the Cromarty specimens, somewhat exceeded a foot. A few detached plates from Orkney, in the collection of Dr Traill, must have belonged to an individual of fully twice that length.

CHAPTER IV.

The Elfin-fish of Gawin Douglas.-The Fish of the Old Red Sandstone scarcely less curious.-Place which they occupied indicated in the present Creation by a mere Gap.-Fish divided into two great Series, the Osseous and Cartilaginous. -Their distinctive Peculiarities.-Geological Illustration of Dr Johnson's shrewd Objection to the Theory of Soame Jenyns.-Proofs of the intermediate Character of the Ichthyolites of the Old Red Sandstone.-Appearances which first led the Writer to deem it intermediate.-Confirmation by Agassiz.-The Osteolepis.-Order to which this Ichthyolite belonged.-Description.-Dipterus.-Diplopterus.—

Cheirolepis.-Glyptolepis.

Has the reader ever heard of the "griesly fisch" and the "laithlie flood," described by the minstrel Bishop of Dunkeld, "who gave rude Scotland Virgil's page?" Both fish and flood are the extravagancies of a poet's dream. The flood came rolling through a wilderness of bogs and quagmires, under banks "dark as rocks the whilk the sey upcast." A skeleton forest stretched around, doddered and leafless; and through the "unblomit" and "barrant"

trees

"The quhissling wind blew mony bitter blast;"

the whitened branches "clashed and clattered;" the

"vile water rinnand o'erheid," and "routing as thonder," made" hideous trubil;" and to augment the uproar, the "griesly fisch," like the fish of eastern story, raised their heads amid the foam, and shrieked and yelled as they passed. "The grim monsters fordeafit the heiring with their schouts;"-they were both fish and elves, and strangely noisy in the latter capacity; and the longer the poet listened, the more frightened he became. The description concludes, like a terrific dream, with his wanderings through the labyrinths of the dead forest, where all was dry and sapless above, and mud and marsh below, and with his exclamations of grief and terror at finding himself hopelessly lost in a scene of prodigies and evil spirits. And such was one of the wilder fancies in which a youthful Scottish poet of the days of Flodden indulged, ere taste had arisen to restrain and regulate invention.

Shall I venture to say, that the ichthyolites of the Old Red Sandstone have sometimes reminded me of the "fisch of the laithlie flood?" They were hardly less curious. We find them surrounded, like these, by a wilderness of dead vegetation and of rocks upcast from the sea; and there are the footprints of storm and tempest around and under them. True, they must have been less noisy. Like the "griesly fisch," however, they exhibit a strange union of opposite natures. One of their families-that of the Cephalaspis seems almost to constitute a connecting link, says Agassiz, between fishes and crustaceons. They had also their families of sauroid or reptile fishes -and their still more numerous families that unite

the cartilaginous fishes to the osseous. And to these last the explorer of the Lower Old Red Sandstone finds himself mainly restricted. The links of the system are all connecting links, separated by untold ages from that which they connect, so that in searching for their representatives amid the existences of the present time, we find but the gaps which they should have occupied. And it is essentially necessary from this circumstance, in acquainting one's self with their peculiarities, to examine, if I may so express myself, the sides of these gaps,-the existing links at both ends to which the broken links should have pieced,-in short, all those more striking peculiarities of the existing disparted families which we find united in the intermediate families that no longer exist. Without some such preparation, the inquirer would inevitably share the fate of the poetical dreamer of Dunkeld, by losing his way in a labyrinth. In passing, therefore, with this object from the extinct to the recent, I venture to solicit, for a few paragraphs, the attention of the reader.

Fishes, the fourth great class in point of rank in the animal kingdom, and, in extent of territory, decidedly the first, are divided, as they exist in the present creation, into two distinct series, the osseous and the cartilaginous. The osseous embraces that vast assemblage which naturalists describe as "fishes properly so called," and whose skeletons, like those of mammalia, birds, and reptiles, are composed chiefly of a calcareous earth, pervading an organic base. Hence the durability of their remains. In the cartilaginous series, on the contrary, the skeleton contains