62 MR. R. LYDEKKER ON THE [Feb. 19, 
replace it. by Hrquelinnesia. A year later (1887), M. Dollo}, 
having had his attention directed to the circumstance that the name 
Glossochelys had been previously applied to one of the forms which 
were included in his Hrquelinnesia, and also to the American types 
described by Prof. Cope, came to the conclusion that Zuclastes, 
Lytoloma, some of the forms included in Puppigerus, Glossochelys, 
and Erquelinnesia, all belong to one arid the same genus. It was at 
the same time considered that the earlier name Osteopygis might 
also indicate the same form, but since the skull was unknown its 
adoption seemed inadvisable; and it was accordingly proposed that 
the term Huclastes, as being the earliest of those based on the 
evidence of the skull, should be the one to be employed in this sense. 
Unfortunately, however, this arrangement could not be accepted, 
since, as the present writer has pointed out in a communication 
recently made to the Geological Society, the name Euclastes is pre- 
occupied. Accordingly, in that communication it was suggested, 
assuming M. Dollo to be correct in his identification of Lytoloma 
with Hrquelinnesia=Glossochelys, that the former name, as being 
the second earliest of those based on parts of the skull, should be 
adopted. 
In the same communication it was also pointed out that the so- 
called Chelone longiceps, which it seemed incumbent to take as the 
type of the genus Puppigerus, was closely allied to the Bracklesham 
Middle Eocene species originally described as Chelone trigoniceps, 
and that, although the latter differed somewhat in the form of the 
mandibular symphysis from typical forms of Lytoloma, yet these 
two species must be classed in the latter genus, as had been proposed 
by M. Dollo, at the time he employed the name Pachyrhynchus in 
the same sense. 
Having now cleared up this intricate web of synonymy, attention 
may be directed to the features in which Lytoloma differs from 
existing Chelonide, and the opinions which have been held as to its 
affinities. 
In describing the Chelonide of the London Clay, Sir Richard 
Owen included in the term Chelone not only the Edible and the 
Hawksbill Turtles, but also the Loggerhead, which is now generally 
regarded as entitled to generic distinction, and forms the type of the 
genus Thalassochelys, that genus typically differing from Chelone 
in the absence of ridges on the palate and mandibular symphysis’, in 
the greater relative length of the latter, the lower alveolar walls of the 
palate and symphysis, and in the tendency to an earlier obliteration 
ef the vacuities in the plastron, as well as in certain other skeletal 
features which need not be mentioned here. It should be observed, 
however, that all the features in which this genus differs from 
Chelone are those of less specialization. 
In his original description Sir Richard Owen pointed out that the 
specimen under consideration was closely allied in structure to the 
skull of the so-called Chelone planimentum. And it was shown that 
? Ibid. vol. v. p. 261 (1888), and Bull. Soc. Géol. Nord, vol. xv. p. 114 (1889). 
® These ridges are present in the Mexican Loggerhead. 
