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Summary.

A new fish-fauna is described from the Middle Culm (barren Coal) Measures of Bude, North Cornwall, comprising three species, of which two, the Acan-thodian Acanthodes wardi Egerton and the Palaeoniscid ElonicMhys aitkeni Traquair, are already well known and have a fairly wide distribution in the English Coal Measures. The third form belongs to a very distinct new genus and species, Cornuboniscus budensis, which, while a typical Palaeoniscid in its fusiform shape, heterocercal tail, and in most other features of its external anatomy, differs from all normal members of that group in having a paddlelike pectoral fin supported by a uniform row of radials but without basal elements. The structure of this fin is compared with those of the aberrant Lower Carboniferous genus Tarrasius and the living Polypterines, and it is tentatively suggested that Cornuboniscus may be a survivor from the original normally shaped Palaeoniscoid stock which, after acquiring the characteristic pectoral fins, gave rise subsequently to degenerate elongated types, of which Tarrasius and the Polypterines represent different branches. The fossils are preserved as external moulds, and are sometimes quite uncrushed, so that many details of the anatomy usually obscured are finely preserved, especially the sensory canal-system and the bones of the rostral region.

Finally, in a survey of the principal types of Actinopterygian pectoral fins it is suggested on the evidence of the development of these organs that the Palseoniscoids must have divided very early into four groups, and an attempt is made to show how the principal types of pectoral fins in existing Actinopterygian fishes might have been derived from the fins in those groups.