1889. ] CHELONIAN GENUS LYTOLOMA. 61 
bridge, and figured by Sir Richard Owen in plate ix. of the 
memoir cited, under the name of Chelone planimentum, the descrip- 
tion 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” ’, 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 1868*, which was based on the evidence 
of the shell; Huclastes, dating from the preceding year*, and 
founded on the cranium; Lytoloma (1870), based on the evidence 
of the mandible; and Puppigerus (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 * 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 °, was 
preoccupied ; and in the following year its author’ proposed to 
1 Trans. Amer. Phil. Soc. yol. xiv. pt. i. (1870). 
* Proc. Ac. Nat. Sci. Philad. 1868, p. 147. 
8 Ibid. 1867, p. 39. 
* Ann. Mag. Nat. Hist. ser. 5, vol. viii. p. 227 (1871). 
° Bull. Mus. R. Hist. Nat. Belg. vol. iv. p. 130 (1886). 
° Geological Magazine, dec. 3, vol. iv. p. 270 (1887). 
7 Ibid, vol. iv. p. 893 (1887). 
