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.

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    plate (^i) ; in which it resembles the Cliel. mydas. Both posterior angles of the first neural plates are produced, and truncate to articulate with the second pair of costal plates ; and the second neural plate is quadrangular. In a portion of another carapace of the CJidone lonyiceps the second neural plate (s2) is pentangular, the right anterior corner being produced, and truncate to join with the first costal plate of the right side ; the left posterior corner of the first neural plate (.91) being produced, and truncate, to articulate with the second costal plate of the left side. This structure I believe, however, to be an individual variety. But the characters of the species are exemplified in more constant modifications of the carapace. The succeeding neural plates to the seventh inclusive {s3—s?) are hexagonal, with the anterior lateral border much shorter than the posterior lateral border, as in Chelone mydas, and not of equal extent, as in Chelone hreviceps; they become more equal in the seventh and eighth neural plates, which also decrease in size ; the ninth plate (59) is very small, quadrangular, and oblong, as in Mr. Lowe’s fragment. Only a small portion of the tenth neural plate is preserved in Mr. Bowerbank’s beautiful specimen. The impressions of the horny scutes are deeper, and the lines which bound the sides of the vertebral scutes {v\—vd) meet at a much more open angle than in the Chel. hreviceps, in which the vertebral scutes have the more regular hexagonal form of those of the Chel. mydas. Their relations to the neural plates are nearly the same as in Chel. hreviceps. The plastron (Tab. V, fig. 2) is more remarkable than that of the Chel. brevicejjs for the extent of its ossification ; the central cartilaginous space being reduced to an elliptical or subquadrangular fissure. The four large middle pieces hyosternals {Jis) and hyposiernals (ps), have their transverse extent relatively much greater as compared with their antcro-posterior extent, than in the Chel. hreviceps; and this might be expected, in conformity with the broad character of the bony cuirass indicated by the carapace. The median margins of the hyosternals {hs) are developed in short toothed processes, along their anterior three fourths; the median margins of the hyposiernals IPS') have the same structure along nearly their whole extent; the intermediate space between the smooth or edentate margins of the opposite bone is ten lines; the expanded end of the long coracoid (52) is seen projecting into this space. The xiphisternals {ws) are relatively broader than in Chel. hreviceps, or in any of the existing turtles ; and are united together, or touch each other, Ijy the toothed processes developed from the whole of their median margins. The entosternal piece is broad, flat on its under surface, and is likewise dentated at its sides. The outer surface of each half of the plastron inclines, as in the Chelone mydas, towards a submedian longitudinal ridge. The breadth of the plastron, in the s])ecimen figured (fig. 2), along the median suture, uniting the hyosternals and hyposternals, is six inches : the narrowest antero- posterior diameter of the conjoined hyosternals and liyposternals is two inches nine lines