OCR Text |
Show 538 MR. A. SMITH-WOODWARD O N T H E [June 23, is represented in Plate XLVII. fig. 3. This bone is of an elongated triangular form, the apex directed anteriorly, and the short base supporting the rays of the fin; it exhibits a little rounded process at the posterior extremity of the inner border, for articulation with its fellow of the opposite side. The pelvic fin is, as usual, somewhat smaller than the pectoral, though still tolerably robust; and its characters are well seen in the original of Plate XLVI. fig. 1. It is opposed to the hinder part of the dorsal, and consists entirely of soft jointed rays, to the number of about 12 in R. buccalis. The dorsal fin is relatively short, and is supported upon a series of strong interspinous bones, of which the most anterior has the widest expansion (R. brama, Plate X L V I . fig. 1). In front, there are about three small spinous rays, followed by two others of larger size ; but the maximum length is attained by the first succeeding soft ray, and from this there is a gradual shortening backwards. In one species, R. latus, the anterior soft ray is extraordinarily powerful, and divided for more than half its length by closely approximated, oblique sutures. There is no trace of an adipose dorsal fin, notwithstanding the perfection with which some of the soft parts are preserved. The anal fin is very small, and the rays in R. buccalis are about 10 in number; these are much divided, as shown in Plate X L V I . fig. 1. The caudal fin, as already mentioned, is deeply forked, and the median rays are very short, only slightly extending beyond the much-elongated posterior termination of the body. In one specimen, indeed, probably referable to R. buccalis (no. P 1958 a), the median rays do not constitute more than a little delicate fringe, sharply marked off from the two main lobes of the fin (Plate XLVlI. fig. 2), though this may quite possibly be an abnormal appearance due to tbe circumstances of fossilization. The scales are preserved in almost every specimen, but it is only rarely that they are well displayed, owing to abrasion and fractures produced in the removal of the surrounding stony matrix. They are deeply imbricated, but it does not seem possible in any case to determine the number either of the transverse or longitudinal series ; nor can anything be stated with certainty as to the variation in size in different regions. The exposed portion of each scale is beautifully ornamented with radiating ridges, which are strongest near the periphery (Plate XLVI. fig. 6 ); and these sometimes impart to the hinder border of dilapidated examples the appearance of being ctenoid. The superficial layer of the scales, however, is nearly always destroyed. The lateral line is only observed where the ornamented portions of the scales are broken away, and would thus not be visible in the living fish. A small " axillary appendage," of elongated form, is to be noted in one or two specimens above the pectoral fin (Plate X L V I . fig. 7). And, lastly, there is the interesting fact that the dorsal and caudal fins are covered to some extent by smaller scales than those investing the body, these being extremely thin and exhibiting no markings beyond the concentric lines of growth (B. M. no. 28616). |