On the Genus Pleuracanthus , Agass., including the Genera Orthacanthus , Agass. and Goldf., Diplodus , Agass., and Xenacanthus , Beyr

Abstract

Hitherto specimens of Pleuracanthus have not been discovered in this country which would serve to illustrate the general characters or zoological position of this genus of fossil Fish. Teeth of Diplodus , almost invariably associated with the spines named Pleuracanthus , Ag. and Orthacanthus , Ag., are found in all the great coal-fields. In Staffordshire, Scotland, Lancashire, and Yorkshire, wherever fish-remains are found, there is some proportion of specimens of these genera. All the examples recorded are from the Coal-measures. Though in England we have only the teeth and spines fossil, in Germany and Bohemia several examples have been discovered in which the whole of the fish is preserved. These specimens appear to be higher in the geological series, and have been relegated to certain passage-beds between the Coal-measures and the Permian, and to the Permian rocks themselves. The ichthyodorulite Pleuracanthus lœvissimus was described by the late Prof. Agassiz, in his ‘Recherches sur les Poissons Fossiles,’ from an imperfect specimen obtained from the coal-shales of Dudley. On page 330 of the same classical work, whilst discussing the “défenses des Raies,” a second spine is mentioned as somewhat resembling Pleuracanthus , and, in all probability, related to it. It was named Orthacanthus cylindricus , and is figured in the third volume, plate 45. figs. 7-9 ; but the description was deferred to a supplementary volume, which, unfortunately, has never been written. At the same time that these spines were discovered, there were also found a number of fossil teeth, which were described and figured by Prof.