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Show 60 MR. R. LYDEKKER ON THE [Feb. 19, 1. On a Skull of the Chelonian Genus Lytoloma. By R. LYDEKKER, B.A., F.Z.S., F.G.S., &c [Eeceived January 28, 1889.] (Plates VI. & VII.) In the year 1849 Sir Richard Owen, in his ' Monograph of the Fossil Reptilia of the London Clay,' Part I. Chelonia, published by the Palaeontographical Society, described and figured (p. 27, pi. xi.) the imperfect skull of a large Marine Turtle from the Lower Eocene London Clay of Harwich, then in the possession of the late Prof. Thomas Bell, under the name of Chelone crassicostata. That species, it may be observed, was founded on the evidence of the shell, and it will be unnecessary on this occasion to enter on the question as to whether the specific association of the skull and shell is or is not correct. In that plate the specimen is figured of two thirds the natural size ; one view showing the frontal aspect of the cranium, a second the right side, and the third the inferior aspect of the mandible, which is retained in its natural position. When the specimen was figured only the frontal aspect of the skull and the inferior and part of the lateral surfaces of the mandible were exposed, the whole of the base and occipital region of the cranium being concealed by the hard rock of the septarian nodule in which the specimen had been embedded. Moreover, on the frontal aspect of the cranium nearly all the outer shell of bone is wanting, the contour being mainly indicated by a cast of the inner surface of the cranial bones. In the year 1863 this specimen was purchased, together with the remainder of Prof. Bell's collection from the London Clay, by the British Museum. There it has remained in its original condition until the beginning of the present year, when, with the permission of Dr. Woodward, the Keeper of the Geological Department, I put it into the skilled hands of Mr. R. Hall, assistant mason in that Department, by whom the skull of Miolania recently described by Sir Richard Owen in the ' Philosophical Transactions' was so skilfully developed. An equally successful result has rewarded his patience and skill in the present instance, and by carefully chiselling away the extremely hard matrix from the base of the specimen, the whole of the palatal and occipital aspects of the cranium, with the exception of that portion concealed by the mandible, is revealed in as perfect a condition as in any recent skull. Indeed, I am unacquainted with any other specimen of reptilian remains from the London Clay in which the bones are so perfectly preserved, and have such a sharp and fresh appearance. Since this skull indicates a genus of Turtles totally distinct from all existing types, the only cranial evidence of which is presented to us, so far as English examples are concerned, by the present specimen and another skull preserved in the Woodwardian Museum at Cam- |