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Show •r>40 MR. A. SMITH-WOODWARD O N T H E [June 23, are short and of equal size, and the vertical extent of the operculum is about twice its antero-posterior measure. The first soft ray of the dorsal fin is very robust and divided by numerous, closely approximated, transverse sutures. Systematic Position. Finally, it remains to determine the systematic position of the genus under consideration. By Agassiz1, Rhacolepis was regarded as a Percoid, probably because the scales had the appearance of being ctenoid, for he had already observed the abdominal situation of the pelvic fins, which would rather point towards a relationship with other types. More recently, Dr. Gunther 2 has quoted the genus as one of the Berycida?; and these are the only two expressions of opinion in regard to the affinities of Rhacolepis that I have succeeded in discovering. A glance at the fossils now made known, however, renders it obvious that we are here concerned with a truly physosto-mous fish ; and it is in this primitive division of the Teleostei that we must look for its nearest living representatives. As kindly pointed out to me by Dr. Gunther, some features displayed by these fossils are curiously similar to those of certain Characiuoids still inhabiting the fresh waters of Brazil. The scales, for example, have an especially Characinoid aspect, and the large size of the circumorbital bones is also a prominent character of the fishes of this family. But the great number of the branchiostegal rays, the peculiarities of the tail, and the fact that these fossils are accompanied mostly by marine forms, are circumstances that seem to point in another direction. The discovery of an " axillary appendage" in some of the specimens, indeed, suggests affinities with the Elopine and Chanine sections of the Clupeidae ; and it is with the first of these groups that I would venture to associate the genus. Elops and its allies are marine types; their bodies exhibit but little lateral compression ; their posterior circumorbitals are very large; their branchiostegal rays are generally numerous; and the tail in these forms almost precisely parallels that of the ancient Rhacolepis. The correspondence is thus so close that there can be no doubt as to the correctness of the determination. It is, in fact, difficult to satisfactorily distinguish the Brazilian fossil from some other Elopine genera already recognized ; for, in dealing with extinct forms, the imperfection of the palaeontological record often prevents any very precise comparisons. Taking first the living genera, Megalops may be said to differ especially in possessing a long anal fin, a distinct lateral line, and villiform teeth ; while Elops seems to be separated by little beyond the conspicuous character of the lateral line, and the absence of small scales on the dorsal and caudal fins. Among fossil allies, Elopopsis 3 has a more power- 1 L. Agassiz, Edinb. New Phil. Journ. vol. xxx. (1841), p. 83; Rech. Poiss. Foss., Synoptical Table, vol. i. p. xliv. 2 A. Giinther, ' Study of Fishes,' 1880, p. 421. 3 J. J. Heckel, ' Beitr. Kennt. foss. Fische Oesterreichs,' 1656, p. 65. |
