| OCR Text |
Show 1894.] SALMONOID FISHES OF THE ENGLISH CHALK. 659 the exposed portion of the scale sometimes shows only the concentric lines of growth, sometimes is ornamented with very fine closely-arranged radiating lines of tubercles. The latter ornamentation is probably normal and varies with the state of abrasion of the fossil. The scales of the lateral line are not enlarged; the course of the sensory canal is marked by a feeble ridge and a notch in the hinder border of most of the scales. 2. ELOPOPSIS CRASSUS. (Plate XLIII. figs. 1, a-c.) Osmeroides crassus, F. Dixon, Geol. & Foss. Sussex, p. 376 (1850) ; A. S. Woodward, Proc. Geol. Assoc, vol. x. p. 322 (1888). The name of Osmeroides crassus was given by Dixon to a unique specimen from the Chalk of Sussex now in the Brighton Museum, but the fossil has hitherto been only briefly noticed without detailed description. The writer has thus availed himself of the kindness of Henry Willett, Esq., and the ex-Chairman of the Museum Committee (EdAvard Crane, Esq.), to examine the original specimen more closely. It comprises the head with the anterior part of the abdominal region of a large fish, m u ch fractured and crushed and exhibiting part of the pectoral fin on the left side. The right side of the head is represented in PI. XLIII. fig. 1; an upper view of the ethmoidal region is given in fig. la ; and separate drawings of the left premaxilla and dentary are given in figs. 1 b, c. The superficial bones exhibit no ornamentation, merely the lines of growth and in places sensory canals. The cranial roof is much crushed and fractured and thus too imperfect for description. The great extent of the frontals, however, is well shoAvn, and the much-expanded and truncated ethmoid (fig. 1 a, eth.) is completely preserved. The postorbital plates (fig. 1, pt.o.) cover the cheek between the orbit and the preoperculum, and there are also remains of well-developed suborbitals (s.o.). The premaxilla (figs. 1, 1 b, pmx.) is relatively small, elongate-triangular iu shape, and furnished on its oral margin with a close series of small conical teeth. Within the mouth, and apparently fixed on the same bone, are also two much-enlarged teeth, laterally compressed but without trenchant edges ; the foremost, placed at the anterior end of the bone and shown only by the base, is the smaller of the two; the second, well-preserved on each side, occurs at about the middle of the bone. In the fossil the anterior ends of the premaxillae are widely separated, but this may be due to crushing. The maxilla (fig. 1, mx.) is very large, extending backwards beyond the orbit, and overlapped above by either one or two supramaxillary bones (s.mx.), which are too much crushed for description. The oral margin of the bone is convexly arched, and in the fossil curves slightly inwards; it bears a single regular series of very short and stout conical teeth, larger than the marginal teeth of the premaxilla, and there are appearances of a second series of smaller teeth occuring immediately within. The dentary bone of the mandible (fig. 1 c) is deep behind and tapers rapidly to an almost pointed symphysis; it bears a single series of well-spaced, large, conical |
