I am acquainted with four species of _Coccosteus_--_C. decipiens_, _C. cuspidatas_, _C. oblongus_, and a variety not yet named; and many more species may yet be discovered.[N] 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. decipiens_ 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 keystone 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. [Footnote N: A fifth species has been named _C. maximus._] 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 that minstrel Bishop of Dunkeld "who gave rude Scotland Virgil's page?" Both fish and flood are the extravagances 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;"