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Show 1869 ] DR. J. E. GRAY ON THE TORTOISES. 209 I have since obtained the skull of Chelodina colliei. It does not render necessary any alterations in the system ; but I would propose that the place of the genus (Chelodina) in the series should be rather altered : instead of following Hydraspis in Hydraspidina, I think that it had better be arranged before it in that tribe, as the skull is more depressed and has a more slender lower jaw, and many other characters render it intermediate in form between the genera Hydraspis and Chelys. Fig. 17. Chelodina colliei. Fam. TRIONYCHIDAE. W h e n m y " Revision of the Species of Trionychidce " was read, on the 23rd February, 1864 (see P.Z.S. 1864, p. 76), I was in doubt whether the alveolar surface of the jaws of these animals did not change in form as the animal increased in age, this doubt being caused by receiving from West Africa skulls from the same locality which chiefly differed iu size and in the form of the alveolar surface. The British Museum has since received other specimens from West Africa; and after examining them I a m satisfied that the skulls referred to belonged to two species, and that the difference of form and structure above mentioned is permanent, and found in young speci- |