The Quarterly journal of the Geological Society of London (1904) (14785036505)

Identifier: quarterlyjourna601904geol (find matches)

Title: The Quarterly journal of the Geological Society of London

Year: 1845 (1840s)

Authors: Geological Society of London

Subjects: Geology

Publisher: London (etc.)

Contributing Library: Smithsonian Institution Libraries

Digitizing Sponsor: Biodiversity Heritage Library

Text Appearing Before Image:

aspect on a detached piece of chalk (fig. 3). The median row ofvery small teeth is scarcely visible in the fragment just mentioned,the large teeth of the first paired series being crushed together toobscure it, but it is shown in back-view (fig. 3 a, 0). Of the firstpaired series (1) three teeth are preserved on the right and six onthe left side, all in natural sequence. They are about as large asthe teeth of the same series in the opposing jaw. The two or threehindermost teeth (fig. 4) correspond with those ordinarily forming >>< . 1 o o ■~o CDO o ci

Text Appearing After Image:

w 0 m H H 341 31 Vol. 60.) JAWS OF PTYCIIODIS FKOM THE CHALK. 135 this series in P. decurrens, but as they are traced forward towardsthe eud of the S3mphysis, they become shorter in proportion to theirwidth and more obliquely distorted, while their median coronalelevation is smaller (fig. 5). The remaining lateral teeth are moreor less displaced, but they are clearly arranged in six paired seriesaltogether (fig. 2); and near the back of the symphysis the teethhave the following transverse measurements (in millimetres):—o, 4 ; i, 6*5 : n, 5 ; in, 4 ; iv, 3*5 ; v, 3 ; vi (?). The specimen therefore proves that, notwithstanding the powerfulnature of the grinding-dentition of Ptychodus and the straightnessof its transverse rows, the supporting jaws had not assumed thepeculiarly-effective disposition characteristic of the living Mylio-batidae, as I formerly supposed. Although it is quite likely that theangle between the mandibular rami seen in fig. 2 (PI. XV)

the quarterly journal of the geological society of london 1904 book illustrations natural history geology high resolution images from internet archive united kingdom

1904

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