OCR Text |
Show 502 ME. A. SMITH WOODWAED ON EXTINCT directed process. The left maxilla (mx.) is completely preserved slightly arched in form, with a small ascending process near its anterior end, and a little expansion posteriorly. Of the right maxilla only a fragment of tbe anterior end remains. The pre-maxillae are not shown, but tbe bone labelled "? barbel axis "in Cope's original specimen may be one of them. No teeth are exhibited in any part of the mouth. The preoperculum (p.op.) has a large lower hmb and is much expanded at the angle. The operculum (op.) is imperfect above, but evidently trapezoidal in form and somewhat deeper than broad. The suboperculum (s.op.) is deeper bebiud than in front, and exhibits four deep clefts in the lower half of its binder border. Small scales can be observed enveloping all the head and opercular bones. The vertebral centra are much constricted and strengthened with small irregular longitudinal ridges. The ribs are remarkably slender, apparently supported by stout processes from the centra; while the separate neural spines in the anterior half of the abdominal region are expanded into thin narrow laminae. The last vertebra of the tail (PL XVIII. fig. 2) bears an upw7ardly-turned double style, and there are seven expanded haemal arches at the base of the caudal fin, the lowest apparently connected with the penultimate vertebral centrum, the next three with the last centrum, and the upper three with the terminal style. It is also worthy of note that the neural arch in the three vertebras preceding the last is forked from the base. Intermuscular bones are seen above the vertebral column throughout, and below it in the caudal region. The fins are as described by Cope, except that the pelvic pair is much larger than indicated in the original specimens. The scales are precisely similar in shape and denticulation to those of the existing Gonorhynchus. 2. NOTOGONEUS SQUAMOSSEUS. (Plate XVIII. figs. 3, 4.) 1818. Cyprinus squamosseus, H . D. de Blainville, Nouv. Diet. d'Hist. Nat. vol. xxvii. p. 371. 1844. Sphenohpis squamosseus, L. Agassiz, Poiss. Foss. vol. v. pt. i. p. 13, pt. ii. p. 87, pl. xlv. Formation and Locality. Upper Eocene; Aix-en-Provence, Prance. The so-called Cyprinus or Sphenohpis squamosseus is represented in the British Museum by several specimens, which, taken together, display nearly all its essential characters. The head with opercular apparatus is relatively much larger than in Notogoneus osculus, its length exceeding the maximum depth of the trunk, and contained only about four times in tbe total length of the fish; the vertebral centra are also much shorter ; otherwise its specific characters seem to be identical with those of the American fish. The best-preserved head belongs to a specimen wanting part of the abdominal region and the caudal fin, and is shown of two-thirds the natural size in Pl. XVIII. fig. 3. It is unfortunately very imperfect, but the enveloping small scales (s.) are exposed in a narrow band, both above and below. The much-fractured |