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Show 558 ON A GIGANTIC EXTINCT SPECIES OF MYLIOBATIS. [June 20 connecting the two. A broad streak of orange colour extends along the inner margin. The underside of the body is similar to R. keithloa, but on the upper surface the head and thorax are a bright blue-green, with the body dark brown. Hah. Angolares. Expanse 2\ inches. PTERYGOSPIDEA FLESUS. Tagiades flesus (Fabr.); Kirby, Syn. Cat. Diurn. Lepid. p. 635. PARNARA NISO. Parnara niso (Linn.) ; Kirby, Syn. Cat. Diurn. Lepid. p. 597. 3. On the Dentition of a Gigantic Extinct Species of Myliobatis from the Lower Tertiary Formation of Egypt. By A. S M I T H W O O D W A R D , F.Z.S. [Eeceived June 20, 1893.] (Plate XLVIII.) The Skates of the family of Myliobatidse are well known to attain a great size, but few examples even of the dentition of the largest specimens are preserved in museums. It is therefore of much interest to record that the British Museum has lately received from Surgeon-Captain E. H. Penton a good example of the jaws of one of the most gigantic extinct species of Myliobatis, discovered in the Lower Tertiary Limestone of the Mokattam Hills, near Cairo, Egypt. So far as the present writer is aware, this is the largest specimen of the dentition of Myliobatis that has hitherto reached any museum. Each jaw is in a separate piece of limestone, but the two portions are known to have been found in association ; and, as usual in the Myliobatida?, one dentition (lower) is flat, while the other (upper) is much bent from front to back. Of the lower jaw, partly shown in the figure (Plate XLVIII. fig. 2), about 17 series of plates are preserved, 10 being worn; while of the upper jaw (fig. 1) only 6 series remain. The unworn teeth are almost smooth, being marked only by short feeble longitudinal striae or rugse. In both jaws the oral surface is arched from side to side, very gently in the lower, more strongly in the upper jaw, as well shown in the sections figs. 1 a, 2 a. The principal teeth are very slightly arcuated and not strongly reflexed at the extremities; and the narrow lateral teeth have their long axes directly antero-posterior, not oblique. As an abnormality, it is also interesting to note in the upper dentition that the two outer lateral series are fused together on one side, while the two inner lateral series are similarly fused on the other side. |