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Show 1889.] ON SOME EOCENE SILUROID FISHES. 201 3. A Contribution to tlie History of Eocene Siluroid Fishes. By E. T. N E W T O N , F.G.S., F.Z.S. [Received March 14, 1889.] (Plate XXI.) The pectoral and dorsal spines of Silurpid fishes from Brackle-sham, which were referred to the genus Silurus by Dixon (21), have recently been studied by Mr. A. Smith Woodward (12), who has shown the improbability of these remains belonging to the temperate genus Silurus and the close relationship existing between them and the widely distributed tropical genus Alius. In addition to the spines and pectoral arch, named by Dixon Silurus egertoni, Mr. S. Woodward has called attention to several other specimens, some from the Upper Eocene of Barton, preserved with the types in the British Museum, among which are bones of the skull and notably some large and characteristic supraoccipitals, one of which he figures ; these he also refers to Arius egertoni. Some smaller spines with a double curvature, from Barton, he places in a new species, Arius (?) barlonensis. The Museum of Practical Geology now possesses the greater part of a skull from the Eocene beds of Barton (Plate XXI. figs. 1, 2, 3), which confirms in a most satisfactory manner Mr. S. Woodward's reference of the Eocene Siluroids to the genus Arius. The skull is somewhat crushed, but the bones are still in position, and by careful manipulation both the upper and under surfaces have been exposed. The ethmoid, prefrontals, and part of the supraoccipital are wanting, and on the right side the temporal region is broken, but on the left only one of the temporal plates is lost. All the bones of the upper surface, which are preserved, are ornamented with rounded granules, and these in nearly all cases radiate from an ill-defined centre towards the margins of the bone. No distinct f-utures can be seen, but the ornamentation being less strongly marked towards the edges of the bones, the boundaries can be fairly well made out; the dark lines in the figure indicate these boundaries, which agree in the main with the positions of the sutures in the recent specimen with which it has been compared. The frontals (fr.) occupy the anterior part of the specimen ; they are narrow posteriorly and meet each other in the middle line for about half their length. The median point of the supraoccipital projects for a short distance between their hinder extremities. Anteriorly a wide and deep depression occupies the median portion of the frontals, and at the bottom of this depression a long cleft separates their inner margins. Each bone is in front divided into two parts, the outer of them no doubt joined the prefrontal and the inner the ethmoid, as in the recent Arius. Behind and on the outer side, each frontal joins a plate (sp.ot.) 1 These numbers refer to a list of works given p. 20G. |
