OCR Text |
Show 176 DR. A. S. WOODWARD ON EXTINCT [Mar. 5, me that the relative development of the mandibular beak varies considerably in the Cryptodiran genus Chelone and in the Pleurodiran genus Sternothcerus, while some species of Podocnemis have two marginal palatal ridges, others have only one. I therefore conclude that there is not yet sufficient reason to separate the South American species now made known from the genus Miolania, hitherto discovered only in the Australian region. It must be regarded merely as forming a very distinct species, characterized by the much-depressed form of the cranium, the enormous size of the occipital crest, the triangular shape of the postero-lateral " horns," the simple rounded ridge on the palate, and the total absence of an internasal septum. It may be appropriately named, following Ameghino, Miolania argentina. It will also be observed that Mr. Boulenger's determination of the Pleurodirau nature of the genus Miolania x is now completely established. II. AN EXTINCT OPHIDIAN, DINILYSIA PATAGONICA, gen. et sp. nov. (Plate XX.) Mr. Roth's discovery of a fossil Ophidian in the red sandstone of Neuquen, associated with typical Mesosuchian Crocodiles, has already been recorded2; but the unique specimen referred to has not hitherto been studied. It comprises the greater part of the skull and mandible, and fragmentary remains of the anterior half of the vertebral column ; the cranium being in an especially good state of preservation. The skull (Plate X X . figs. 1, la) is long, narrow, and depressed, with the cranial region as long as the facial region. It seems to have been widest at the occiput, where the otic region is very massive ; and the maximum compression is immediately in front of this, where the parietals rise into a prominent sagittal crest. The constitution of the hinder part of the skull is best seen on the left side of the fossil, where there is only one slight antero-posterior crack (x) in the bones. The right postero-lateral angle, on the other hand, is fractured and displaced downwards. The foramen magnum, which is filled with matrix, is completed above by the exoccipitals (ex.occ), which meet in the middle line. They are directly continuous on each side with a great, expanded piece of bone (op.), which curves backwards as well as outwards and abuts upon the bone at the upper end of the quadrate. This expansion of the exoccipital is probably the opisthotic, which is similarly fused with the exoccipital in Lacertilia and the extinct Mosasaurs. Above the exoccipilals is the short but laterally-extended supraoccipital (s.occ), which completes the sagittal crest behind. Its lateral extremity on the left is in contact with a small trace of bone (o.), 1 G. A. Boulenger, " O n the Systematic Position of the Genus Miolania, Owen (Ceratochclys, Huxley)," P. Z. S. 1887, pp. 554, 555. Also " Remarks in reply to Dr Baur's Article on the Systematic Position of Miolania," Ann. Mag. Nat. Hist. [0] vol. iii. 1889, pp. 138-141. 2 A. Smith Woodward, Anales Mus. La Plata-Paleont. Argent, no. iv. (1896), p. 1- |