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Updated: May 1, 2025
"Yes; and you will observe that these fossil fishes have no identity with any living species. To have in one's possession a living specimen is a happy event for a naturalist." "But to what family does it belong?" "It is of the order of ganoids, of the family of the cephalaspidae; and a species of pterichthys.
The pterichthys has also strong bony plates over its body, arranged much like those of a tortoise, and has a long tail; but its most remarkable feature, and that which has suggested its name, is a pair of long and narrow wing-like appendages attached to the shoulders, which the creature is supposed to have erected for its defence when attacked by an enemy.
Among the anomalous forms of Old Red fishes not referable to Huxley's Crossopterygii is the Pterichthys, of which five species have been found in the middle division of the Old Red of Scotland. Some writers have compared their shelly covering to that of Crustaceans, with which, however, they have no real affinity.
Some of the fossils of this system, the cephalaspis, coccosteus, pterichthys, holoptychius are, in form and structure, entirely different from any fishes now existing, only the sturgeon family having any trace of affinity to them in any respect. They seem to form a sort of connecting link between the crustacea and true fishes.
It appears that in the imperfect condition of the vertebral column, and the inferior situation of the mouth in the pterichthys, coccosteus, &c., there is an analogy to the form of the dorsal cord and position of the mouth in the embryo of perfect fishes. The one-sided form of the tail in the osteolepis &c. finds a similar analogy in the form of the tail in the embryo of the salmon.
The number of species of fish already obtained from the middle division of the Old Red Sandstone in Great Britain is about 70, and the principal genera, besides Osteolepis and Pterichthys, already mentioned, are Glyptolepis, Diplacanthus, Dendrodus, Coccosteus, Cheirancanthus, and Acanthoides. Cephalaspis Lyellii, Agassiz. Length 6 3/4 inches.
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