193.) HAY—EXISTING GENERA OF THE TRIONYCHIDA. 271 
both Aspidonectes and Pelodiscus, was not repeated in his work 
of 1843. 
We may then, it appears to the writer, regard it as established 
that the type of the genus Zyconyx is the species granosus; of 
A spidonectes, the species ¢riunguis ; of Platypeltis, the species ferox ; 
of Pelodiscus, the species sinensis, and of Amyda, the species 
subplana. 
We must now consider how these determinations are to affect the 
work of subsequent writers, especially that of Gray, Agassiz, and 
Baur. 
In 1844, Gray (Cat. Tort., Croc. and Amphib., p. 46) established 
the new genera Zyrse, Dogania and Chitra, besides propagating his 
erroneous uses of the terms Zyrionyx and Emyda. The type of 
Chitra is Trionyx tndica Gray, and this genus is yet recognized as 
avalid one. The type of Dogania is naturally the only species 
mentioned under it, swdp/anus; but this had already in 1836 been 
made by Bonaparte the type of Amyda, from which fact it follows 
that Dogania is a synonym of Amyda. Under Zyrse there were 
named six species, but no type was selected. In his later publica- 
tions Gray dropped from Zyrse all the species originally included 
under it, except ¢riunguis (nilotica). We must then suppose that 
he regarded this species as the type of the genus; but this was, as 
we have seen, the type of Aspidonectes, made so by Bonaparte in 
1836. Zyrse, therefore, becomes a synonym of Aspidonectes. 
Agassiz accepts Zrionyx ferox as the type of Platypeltis. While 
rejecting Pe/odiscus as a valid genus, he correctly states that it rests 
on Zrionyx sinensis Wiegm. He does not say what he regards as 
the type of Aspidonectes, but he includes under it Z7zonyx spint- 
ferus. Amyda, he states, has for its type LeSueur’s 7rionyx muti. 
cus; and he tells us that this generic name was vaguely applied by 
Fitzinger to one of his genera. “As we have seen, no type was indi- 
cated for Amyda in 1836, but in 1843 Fitzinger names under the 
genus only the species sudp/ana. There certainly was no vagueness 
in this procedure. Furthermore, Bonaparte had already in 1836 
indicated the same species as the type of Amyda. 
As already stated, Dr. Baur regarded the species cartilagineus as 
the type of Aspidonectes and Trionyx muticus as the type of Amyda ; 
whereas Bonaparte in 1836 and Fitzinger in 1843 made ¢riunguis 
(agyptiacus) the type of the former, and swép/anus as the type of 
the latter. Baur recognized Zestudo ferox Schweigg. as the type of 
