OCR Text |
Show 1889.] EOCENE SILUROID FISHES. 205 sented by figure 10, and it will be seen that all the points mentioned as characteristic of the fossil otolith are repeated in this, and it is only in outline that there is any real difference. The projection of the inner margin marked x (fig. 10 b) isiu a depression and does not form a prominent angle as in the fossil (fig. 3 b), and the swelling of the outer margin (y) is, in A. gagorides, placed further backwards than in the fossil. Unfortunately, the otoliths of nearly allied recent species or genera are not available for comparison, and consequently we know nothing of their specific differences. In the collection of Fish otoliths preserved in the Hunterian Museum of the Royal College of Surgeons there are a few belonging to Siluroids, but none of them to genera nearly allied to Arius, and they all differ widely from the otolith of Arius gagorides. The series of otoliths from the Upper Eocene of Barton, preserved in the British Museum, includes many which agree with A. gagorides in these main characters which seem to me to be generic, and these, therefore, I also refer to the genus Arius. Besides differences of size, which in part no doubt are due to age, these otoliths present several distinct forms, which I believe will be found to represent at least three species, in addition to the skull above described. The largest of these (fig. 4) is a little longer and more regularly oval than that found in the Barton skull; its lower surface is also flatter, and its upper surface is raised into an almost conical boss. The second form to be noticed (fig. 5) is smaller, flatter, and more rounded in outline, having the hinder point only slightly produced. The third form (fig. 6) is likewise flat and about the same size as the one last noticed ; in outline, however, it more resembles that of A. gagorides, but the swelling of the outer side (y) is not thrown so much backwards as in that species. There is still another form of Arius otolith to which I should like to call attention. Among the fossils brought from Madagascar by the Rev. R. Baron, and noticed in his paper read before the Geological Society (Mar. 6, 1889), were some small otoliths (fig. 7) which he had collected in the village of Ankoala, where they occurred in some numbers scattered over the surface of the ground. These otoliths bear such a close resemblance to some of those from the Eocene beds of Barton, that they not unnaturally led to the supposition that they also were of Eocene age ; but both these forms are referable to the living genus Arius, which is a widely distributed tropical form, and it seems very probable, therefore, that the Ankoala specimens may prove to be of much more recent origin, and the peculiar conditions under which they were found seem to point to their belonging to a living species. W e have now to consider the relation which the Barton skull and the otoliths above described bear to the specimens referred to Arius eyertoni and to A. ? bartonensis ; and before doing so I may say that I quite agree with Mr. Smith Woodward's reference of the cephalic plates from Bracklesham to the species A. eyertoni; for their |