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Show 662 MR. A. SMITH WOODWARD ON THE SO-CALLED [Nov. 20, clavicle (s.cl.) and the arched clavicle (el.) expanded at its lower end. Posteriorly may also be seen the large scapula (sc), pierced by an oval foramen. The pelvic arch (fig. 6, plv.) is of the ordinary form, the two halves separate, each expanded at the origin of the fin and tapering forwards. It is situated in a remarkably advanced position, for the figured specimen seems to shoAV that the anterior fins represented in the type specimen are truly the pelvic pair ; while each of these fins is very well developed and comprises not less than eight raysl. The dorsal fin (fig. 2, d.f.) occupies about the middle of the back and seems to comprise two or three spinous rays anteriorly. The anal fin is small and remote, consisting of robust rays Avhich are unjointed for a considerable length at their base. The scales are thick, cycloid, and very deeply overlapping; the external markings are merely those produced by the concentric lines of growth, but there are a few traces of radiating lines and crimping in the coATered portion. The peculiar longitudinal elevations, described by Agassiz as marking the course of the " lateral line," are apparently confined to the scales of the caudal region. 4. ACROGNATHUS BOOPS. Acrognathus boops, L. Agassiz, Poiss. Foss. vol. v. pt. i. p. 14, pt. ii. p. 108, pi. Ix. a. figs. 1-4 (1834-44); A. S. WoodAvard, Proc. Geol. Assoc, vol. x. p. 323 (1888). N o new evidence is forthcoming as to this supposed deep-sea Salmonoid. It is represented in the British Museum only by the type specimen and a fragment. Conclusion. In determining the systematic position of these fishes from the English Chalk it is, of course, impossible to refer to the most distinctive external feature by which Salmonoids can be separated from Clupeoids. The nature of the matrix would not admit of the preservation of an adipose dorsal fin, even if it were originally well-developed. Three osteological characters of Osmeroides and Aulolepis, hoAAever, n o w made knoAvn for the first time, combine to suggest comparisons only in one direction, namely, AA"ith the modern genera Elops, Megalops, and their extinct allies. These characters are:-(i.) the union of the parietal bones mesially to the exclusion of tbe supraoccipital from the cranial roof; (ii.) the arched maxilla overlapped aboAe by two large supramaxillary bones ; and (iii.) the presence of a large gular plate. It is true that although in the typical Salmonidae the supraoccipital separates the parietals on the cranial roof, there are rare instances (e.g., Thymallus) in which the parietals are in contact throughout their 1 Since this paper was read the writer has observed a specimen in the Woodwardian Museum, Cambridge (Forbes-Young collection), in which the pelvic fins are beautifully preserved in the advanced situation here described. |