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, 1 
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 colliez. 
Fam. TRIONYCHID. 
When my “ Revision of the Species of Trionychide”’ 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 in 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 am satisfied that the skulls re- 
ferred to belonged to two species, and that the difference of form and 
structure above mentioned is permanent, and found in young speci- 
