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Show 1889.] CHELONIAN GENUS LYTOLOMA. 61 bridge, and figured by Sir Richard Owen in plate ix. of the memoir cited, under the name of Chelone pldnimentum, the description of the newly revealed palatal surface appears worthy of a place in the Society's 'Proceedings.' It is not, indeed, that the chief features of this surface have been hitherto unknown, for they have been described by M . Louis Dollo, of the Royal Museum of Natural History of Brussels, upon the evidence of specimens obtained from the Lower Eocene of Belgium, which are probably specifically identical either with the present form or with the one described as Chelone planimentum. Hitherto, however, M . Dollo has given no figure of the cranium, and I doubt whether any of the Belgian examples can be as beautifully preserved as the present one. It has long been seen that the Chelonians from the London Clay described by Sir Richard Owen under the general term Chelone included many forms which could only be retained in that genus by employing that term in a much wider sense than that in which it is understood by students of recent herpetology. And from the year 1867 onwards a number of generic terms have been proposed for these and allied Chelonians from other deposits, which has resulted in an unusually complex synonymy. The chief features of this synonymy it is necessary to notice in some detail before proceeding to the consideration of the specimen before us. In the year 1870, Prof. E. D. Cope, of Philadelphia, published his well-known " Synopsis of the Extinct Batrachia, Reptilia, and Aves of North America " 1, containing descriptions of the remains of Eocene Chelonians allied to the present form, which were arranged under several generic names, of which some had been first published at earlier dates. The names which it will be necessary to mention are-Osteopygis, dating from 18682, which was based on the evidence of the shell; Euclastes, dating from the preceding year3, and founded on the cranium ; Lytoloma (1870), based on the evidence of the mandible; and Puppiyerus (1870), which was applied to several of the Chelonians from the London Clay described by Sir Richard Owen, Chelone planimentum not, however, being among the number. In the following year Prof. H. G. Seeley 4 proposed to distinguish the last-named species under the generic name of Glossochelys. Thus matters stood till the year 1886, when M . Dollo ° described some Chelonian remains from the Lower Eocene of Belgium, which he regarded as closely allied to Chelone crassicostata and C. planimentum, and proposed to refer, together with these and some other species, to a new genus under the name of Pachyrhynchus. That name, however, as was pointed out in a joint paper by Mr. G. A. Boulenger and the present writer 6, was preoccupied; and in the following year its author7 proposed to 1 Trans. Amer. Phil. Soc. vol. xiv. pt. i. (1870). 2 Proc. Ac. Nat. Sci. Philad. 1868, p. 147. 3 Ibid. 1867, p. 39. 4 Ann. Mag. Nat. Hist. ser. 5, vol. viii. p. 227 (1871). 5 Bull. Mus. E. Hist. Nat. Belg. vol. iv. p. 130 (1886). 6 Geological Magazine, dec. 3, vol. iv. p. 270 (1887). 7 Ibid. vol. iv. p. 393 (1887). |