Volume 1

Monograph on the fossil reptilia of the London clay / by Professor Owen and Professor Bell.

  • Owen, Richard, 1804-1892.
Date:
1849
Catalogue details

Licence: Public Domain Mark

Credit: Monograph on the fossil reptilia of the London clay / by Professor Owen and Professor Bell. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    17/360 (page 1)
    ON TUB FOSSIL REPTILIA OF THE LONDON CLAY. Oii\)^Vi.—CllELONIA. Fam ily—M a r i n a . Genus— Chelone. The majority of the Fossil Clielonians of the Eocene tertiary deposits, defined or described in my ‘ Report on British Fossil Reptiles,’ belong-ed to the marine division of the order, and to the genns Chelone; and as the species of this genus depart least from the ordinary reptilian type in the modification of the Ijones of the trunk, composing the characteristic thoracic-abdominal case of the order, I propose to commence with them those descriptions of the Chelonian reptiles which fall to my share of the present Monograph. In order to facilitate the comprehension of the descriptions and figures of the fossil Clielonians, a brief notice is premised of the composition and homologies of the carapace and plastron, or roof and floor, of that singular portable abode, with which the reptiles of the present order have lieen endowed in compensation for their inferior powers of locomotion or other modes of escape or defence. In the marine species of the Chelonian order, of which the Chelone mjjdas may lie regarded as the type, the ossification of the carapace and plastron is less complete, and the whole skeleton is lighter than in those species that live and move on dry land ; but the head is proportionally larger—a character common to aquatic animals,— and being incapable of retraction within the carapace, ossification extends in the direction of the fascia, covering the temporal muscles, and forms a second bony covering of the cranial cavity : it is interesting to observe, however, that this accessory defence is not formed by the intercalation of any new bones, but is due to exogenous growth from tlie frontals (ii), parietal (7), postfrontals (12), and mastoids (8, see T. I, T. Ill, T. XV). The bony carapace is composed externally of a series of median and symmetrical pieces (fig. 1, ch,, .51—.S'ii,yi//), and of two series of unsymmetrical jiieces (y;/i_s, wi—12) on each side. The median ])ieces have been regarded as lateral expansions of the summits of the iqiper vertebral (neural) spines,* the median lateral pieces as similar * Cuvier, Lecons d’Anatomic Coniparee, tom. i (1799), p. 212.