The exception above alluded to, is a little Malacopterygian fish, rather larger than a Sprat, called the Capelan (Mallotus villosus), which inhabits the banks of Newfoundland, and other parts of the coasts of the northern seas. Fossil specimens of this fish.[566] occur in nodules of indurated marl or clay, on the coast of Greenland.[567] It is supposed that these Ichthyolites are of very recent date: and that similar fossils are in the progress of formation.
[566] See Poiss. Foss. tom. v. pl. lx., in which the skeleton of the recent fish, and specimens of the fossil species, are represented.
[567] Similar fossils have been obtained from the "Drift" on the Saco River, thirty miles north of Portsmouth, New Hampshire. See Lyell’s Second Visit to the United States, vol. i. p. 29.
Ichthyopatolites, or imprints of the pectoral fin-rays of certain fishes. Under this name Dr. Buckland described certain problematical markings observed on a flag-stone from a coal-pit at Mostyn, in Flintshire, and now in the Geological Society’s Museum. It consists of curvilinear scratches or imprints, disposed symmetrically at regular intervals on each side a smooth level space, about two inches wide, which may correspond to the body of a fish, the pectoral fins of which Dr. Buckland suggests were the instruments by which the markings in question were formed.
These scratches follow each other in nearly equidistant rows of three in a row, and at intervals of about two inches from the point of each individual scratch to the points of those next succeeding and preceding it; they are slightly convex outwards, three on each side the median space, or supposed track of the body of the fish. Dr. Buckland, in the memoir referred to, shows that these markings cannot be referable to the imprint of the feet or claws of reptiles, and points out the structure of the bony anterior rays of the pectoral fins, as in certain Siluroid and Lophoid fishes, and in the Climbing Perch (Anabas scandens), or the Hassar (Doras costata), and refers also to the ambulatory movements of the common Gurnard, in corroboration of this opinion.[568]
[568] Proceedings of Geol. Society, vol. iv. p. 204.
Geological Distribution of Fossil Fishes.—From the incidental notices of the geological habitats of the fossil fishes enumerated in our survey of this class of beings, the reader cannot fail to have remarked, that the most recent strata abounded in forms related to the inhabitants of the existing seas and rivers; while the most ancient teemed with species and genera of families altogether extinct, or of prodigious rarity in the recent fauna.
In general terms, it may be stated, upon the authority of M. Agassiz, that the Ichthyolites of the Tertiary deposits approach in their characters to the living genera, but all the species are extinct. The newer Tertiary, as the Crag, contain genera common to tropical seas, as the large sharks (Carcharias), and eagle-rays (Myliobates), &c. In the Eocene, or most ancient Tertiary, as the London and Paris basins, Monte Bolca, &c., many of the Ichthyolites are closely related to recent genera. Of the Chalk fishes, a few only are of recent genera, but the majority are still allied to Tertiary forms. In the Chalk, the Pharyngognathi, Acanthopteri, and Malacopteri are met with as new types; and indications of the Hybodontidæ, Sauroidei, and Cœlacanthi (the last derived from the Devonian, and the other two from the Carboniferous Limestone) appear for the last time.
The ichthyic fauna of the Cretaceous deposits is closely related by the majority of its family groups with that of the series of strata from the Lias to the Wealden, inclusive. In and above the Lias all the ganoid fishes are homocercal. Below the Lias, the genera and species are far more removed from existing types, and almost all are heterocercal.