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The holoptychius is of a flat oval form, furnished with fins, and ending in a long tail; the whole body covered with strong plates which overlap each other, and the head forming only a slight rounded projection from the general figure.
The defensive fin-bones of these creatures are not infrequent at Armagh and Bristol; those known as Oracanthus, Ctenocanthus, and Onchus are often of a very large size. Ganoid fish, such as Holoptychius, also occur; but these are far less numerous. The great Megalichthys Hibberti appears to range from the Upper Coal-measures to the lowest Carboniferous strata. Fusulina cylindrica, d'Orbigny.
BRITISH. Coal-measures of South Wales, with underclays inclosing Stigmaria. FOREIGN. Coal-field of Saarbruck, with Archegosaurus. BRITISH. Mountain limestone of Wales and South of England. FOREIGN. Mountain limestone of Belgium. BRITISH. Yellow sandstone of Dura Den, with Holoptychius, etc. FOREIGN. Clymenien-kalk and Cypridinen-schiefer of Germany.
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.
Palaeontologists have long maintained that the same species which have a wide range in space are also the most persistent in time, which may prepare us to find that some plants having a vast geographical range may also have endured from the period of the Upper Devonian to that of the Millstone Grit. Scale of Holoptychius nobilissimus, Agassiz. Holoptychius, as restored by Professor Huxley. a.
The fringed pectoral fins. b. The fringed ventral fins. c. Anal fin. d, e. It is not improbable that the beds given in this section as Nos. 1, 2, and 3, may all belong to the early part of the period of the Upper Old Red, as some scales of Holoptychius nobilissimus have been found scattered through these beds, No. 2, in Strathmore.
The highest beds of the series in Scotland, lying immediately below the coal in Fife, are composed of yellow sandstone well seen at Dura Den, near Coupar, in Fife, where, although the strata contain no mollusca, fish have been found abundantly, and have been referred to the genera Holoptychius, Pamphractus, Glyptopomus, and many others.
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