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Show 1905.] PRIMITIVE REPTILE PROCOLOPHON. 217 1904) that Mesosaurus is not a Plesiosaur, mainly because the Plesiosaurs seem to have sprung from a land ancestor which had lost its precoracoid and had the Sphenodon type of pelvis, whereas Mesosaurus has evidently sprung from a land-form which retained its precoracoid and had a plate-like pelvis. As Mesosaurus lived in Lower Permian times, it is evident that true reptiles of the Diapsidan phylum existed at a very early period. Only a few of them have so far been discovered, and at present we can only imagine what the structure of many of the early forms was like from what we know of the specialised descendants. Procolophon I believe to be a slightly modified descendant of one of the early Permian Diapsidan types such as that which gave rise to Mesosaurus. The beds in which Procolophon occurs are either Middle or Lower Triassic, but there is reason to believe that Saurosternon is an allied form, and this occurs in beds which are most probably Upper Permian. So that the Procolophonia probably originated in Permian times. The beds in which Telerpeton occurs in Scotland are considerably younger than the Procolophon-beds of S. Africa, being probably Upper Triassic, Rhfetic, or possibly even Liassic. I hope shortly to give a complete account of the structure of Procolophon, and it is to be desired that one of the American workers will do the same for one or other of the Cotylosaurians. We shall then be in a position to realise more clearly what are the relationships of these primitive types to each other. More important Literature. 1. O w e n , R.-Catalogue of the Fossil Reptiles of S . Africa. London, 1876. 2. S e e l e y , H. G.-" On new Species of Procolophon, &c." Q. J. G. S. vol. xxxiv. 1878. 3. S e e l e y , H. G.- " On Pareiasaurus bombidens (Owen), &c." Proc. Roy. Soc. 1888. 4. C o p e , E. D.- " On the Homologies of some of the Cranial Bones of the Reptilia, &c." P. A. A. A. S. xix. p. 13. 5. Z it t e l , K. v.-Handbuch der Palfeontologie. Yol. iii. 6. L y d e k k e r , R.--Catalogue of the Fossil Reptilia and Amphibia in the British Museum. Pt. iv. London, 1890. 7. S e e l e y , H. G.- " Further Observations on Pareiasaurus." Phil. Trans. 1892. 8. B r o o m , R.- " On the Remains of Procolophon in the Albany Museum." Rec. Alb. Mus. vol. i. no. 1 (1903). 9. O s b o r n , H. F.-" The Reptilian Subclasses Diapsida and Synapsida, &c." Mem. Amer. Mus. Nat. Hist. 1903. 10. B o u l e n g e r , G. A.- " On the Characters and Affinities of the Triassic Reptile Telerpeton elginense." P. Z. S. 1904, vol. i. pt. 2. 11. W o o d w a r d , A. S .-Outlines of Vertebrate Palaeontology. 1898. |