Abstract
During five seasons the writer has been investigating the fishes of the Middle Devonian flagstones in the quarry at Achanarras in Caithness. This celebrated quarry, the home ofPalœospondylus, has been long known and has been previously worked by Traquair (1890, 1894), who has described its fauna. There appeared, however, still to be room for a more detailed and intensive examination of the fauna such as could only be produced by a more extended period of work than had so far been given to it. By permission of Colonel Murray-Thriepland, the owner of the estate on which the quarry is situated, I have been able to spend the seasons of 1931–1935 in making a collection, of which a part is now to be described. To the Colonel and to his son Mr Peter Murray-Thriepland I have been indebted throughout for their unfailing interest and assistance. The main part of this account was written in 1934, but was not published owing to the discontinuance of a foreign journal for which it had been accepted. The season of 1935 produced some further material, which has now been incorporated. Meanwhile the writer has had the opportunity of discussing questions relating to the genusDipteruswith Dr Stanley Westoll, who has in preparation a work on the Devonian fishes in general, and is indebted to him for information on several points. Dr Westoll's view that the scales show an alternate deposition and resorbtion of the outer layer together with its bearing on questions of species is here fully adopted (Westoll, 1935).

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