78 DR. J. E. GRAY ON THE TRIONYCHIDE. (Feb. 23, 
organization, both external and internal; but when I printed the 
former catalogue I had only the skulls of three species. I have been 
able to add considerably to the collection of skulls ; but the number 
of known species has also extended, and now the skulls of only about 
half of the species determined on their external form and coloration 
are known, so that I am not able to make the rigorous examination 
and comparison between the skulls that I could wish; and I am by 
no means sure, after what I have seen, and especially after the facts 
stated by Professor Agassiz, that more than one species may not be 
confused under one name, from the species having been simply de- 
termined by their external form and coloration. 
Wagner, in his system, separated the species that had their hind 
legs covered with moveable valves and the margin of the shield bony, 
from those which have the hind legs free and the margin of the disk 
flexible, calling the former Trionyx, and the latter Aspidonectes. In 
my Synopsis of Reptiles in the translation of Cuvier’s ‘ Animal 
Kingdom,’ I retained the name of Trionyx for the latter group (as 
it contained the typical species of the genus), and called the former 
one ELmyda. Dumeéril and Bibron, with the usual habit of the 
French naturalists, gave new names to all the groups, calling the 
first group Cryptopus, and the latter Gymnopus. 
Dr. Peters, when in Mozambique, discovered a Tortoise (which he 
at first called Cyclanosteus, but afterwards Cycloderma) intermediate 
between these two groups, having the hind leg covered with sternal 
valves, and the margins of the shields boneless and flexible. 
I may here observe that I cannot agree to the changes in the no- 
menclature proposed by Professor Agassiz in the ‘ Contributions,’ at 
pp- 396 and 397 ; indeed I am convinced that, if he had studied the 
Indian and Asiatic species as he has the American, he would modify 
his suggestions. 
Fitzinger, in his ‘Systematic Catalogue of Tortoises’? in the 
‘ Annals of the Vienna Museum,’ published in 1836, divided the 77%0- 
nyches with free feet and a flexible margin into four genera, contain- 
ing most incongruous species associated together (for example, T’rio- 
nyx javanicus and T. egyptiacus of Geoffroy and T. indicus of Gray, 
Trionyx muticus, Lesueur, and 7’. subplanus, Geoffroy) in the same 
genus. Sometimes he refers the same species (as, for example, 7. 
egyptiacus, Geoffroy, and 7’. labiatus of Bell, which are only states 
of the same species) to two genera, as the first to Aspidonectes, and 
the latter to Pelodiscus. 
Professor Agassiz truly remarks, “All these new genera are founded 
upon delusive characters, as Gray has already stated, which depend 
only upon the progress of the ossification of the shield, and may be 
observed in specimens of different ages of one and the same species, 
as my numerous skeletons of these Turtles clearly show; moreover 
the difference in the length of the tail is only sexual, the tail being 
very short in the female, and extending beyond the rim of the shield 
in the males of all the species that I know.”—Contrib. 395, 396, 
If the generic names which Fitzinger has given are used, it must 
be with quite a different significance than that attributed to them 
