III.—On the Cranial Structure of an Early Palæoniscid,Kentuckia, gen. nov.

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Abstract
Synopsis: Kentuckia, from the basal Carboniferous, is the earliest bony fish in which neurocranium and dermal skeleton are well known. The dermal bones show that it belongs to the central family Palæoniscidæ of Berg. They have no obvious generalised characters, however, and are chiefly distinguished by a deeply embayed hind margin to the skull roof, no dermohyals and an elongated postorbital bone. These features suggest a greater affinity with the few known Devonian types than with those of the Carboniferous.The neurocranium has a considerable likeness to Watson's Kansas Palæoniscids A and B, and confirm Watson's view that this is the fundamental type of actinopterygian cranium.Kentuckiais slightly more generalised than the others in having a paired myodome and a less excavated dorsal surface. The notochord in all three has a long anterior extension like that shown inPteronisculus(Glaucolepis) of the Eo-Trias by Nielsen. This latter fish is similar to the earlier ones if allowance is made for a greater proportion of cartilage. In the discussion reference is also made to the following: the degree of ossification of these fishes, the nature of the cranial fissure and its homologues, the distribution of the third, fourth, fifth and seventh nerves, and the origin of the cranial wall in the orbitotemporal region.Certain additions are made to Watson's account of Palæoniscids A and B, particularly concerning the interior of the braincase. A new form, C, is also described.

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