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Show 204 MR. E. T. NEWTON ON SOME [Apr- 2, the indentations of the margin are alike in the two forms, but the supraoccipital of the fossil is evidently a shorter and wider bone, and it is uncertain whether it was constricted in the middle or not. The supraoccipital of A. egertoni is only slightly constricted, and it may be that the Barton skull, here described, more resembled that species. Several of the anterior vertebrse of A. gagorides are united to form one mass, in a manner precisely similar to that which obtains in the fossil. The differences above noted show clearly that the recent and fossil forms are specifically distinct, while at the same time the resemblances are sufficiently important to prevent a generic separation ; but there is still some additional evidence which supports this decision in an unexpected manner. While clearing away the matrix from the right side of the fossil skull, where it is broken near the back, I was fortunate enough to find one of the otoliths in place, and this, when extracted, proved to be of a remarkable form (figs. 3, a, b, c), and quite unlike the otolith of any fish with which I was acquainted. When found, this otolith had the more pointed end directed backwards and outwards, with the smooth surface upwards; and as it seemed to be in its natural cavity, for the present this is regarded as its proper position ; but seeing that the otolith of the opposite side is not in its place, and that in the diied skull of the recent species they are loose in the brain-cavity, this may not be correct. The otolith is proportionately large and thick, its upper surface (a) is smooth and convex, while its lower surface (b) is rugose and much more convex. At first sight there appears to be no sulcus acusticus, but probably it is represented by the sinuous groove on the lower surface which passes from the hinder pointed end to the opposite extremity, that is between the two stars in figure 3 b. The rugosity of the under surface is due to a number of concentric striations, or lines of growth, crossed by several radiating ridges which are stronger on the inner than on the outer portion. One of the radiating ridges is especially strong, and forms a prominent angle where it reaches the inner margin, towards the front of the otolith (fig. 3 b, x). The pointed extremity is seen to be notched, a slight groove extending from this both on the upper and lower surfaces (figs. 3 A, b). From this bifid point a shallow groove extends along the outer margin, becoming a mere line towards the front; it is seen in an upper view (fig. 3 a), and is separated from the smooth upper surface by a fine but distinct raised line. A similar otolith to this is figured by Herr E. Koken, from the Oligocene of Headon Hill, Isle of Wight (6), who, having no clue to its affinities, called it Otolithus (incertes sedis) crassus. The close relationship between the recent Arius gagorides and the Barton fossil skull made it particularly desirable to see whether the otoliths would show a corresponding resemblance, and Dr. Giinther very kindly had the otoliths taken out of the skull with which the above comparisons had been made. One of these otoliths is repre- |
