Chap. III. GENERA OF TRIONYCIIIDiE. 395 



and united all the others under the name of Aspidonectes, supposing that the 

 soft marginal dilation of the shield assists in swimming, which is only true in as 

 far as it forms a sharp cut-water, for it is not moved up and down, as are the 

 wings of iJie Skates. 



The two genera proposed by Wagler have since been adopted by all modern her- 

 petologists, who have vied with one another in changing their names, although not 

 to the real advantage of science. Thus Dumeril and Bibron, discarding entirely the 

 old generic names, call Gymnopus the genus which Wagler had named A.spidonectes, 

 and Cryptopus, that for which he had retained the name Trionyx.^ J. E. Gray, 

 on the contrary, restored the name Trionyx to the genus which Wagler had 

 called Aspidonectes,^ and gave a new name, Eiuyda, to Wagler's Trionj'x. In 

 1836, Fitzinger^ introduced further generic distinctions in this family, calling Tri- 

 onyx the same genus for which Wagler had retained that name ; Aspidonectes, 

 the Trionyx javanicus and oegyptiacus of GeofFr. and the Trionyx indicus of Gray, 

 and proposing three iiew genera, one under the name of Platypeltis for the Tr. 

 ferox, Schw., and spinifer and ocellatus, LeS. ; another under the name of Pelodis- 

 cus for the Tr. smensis, Wie(/., and the Tr. labiatus, Bell; and a third one, for 

 which Fitzinger revives the old name Amyda for the Tr. subplanus, Gcoffr., and 

 the Tr. muticus, LeS^ But all these new genera are founded upon delusive char- 

 acters, 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 oiily sexual ; the tail 



* Erpct. gciKT. vol. 2, p. 472 and 475, on the as he pleased the genera he first recognized ; and a* 



ground that Aspidonectes and Trionyx have both he chose to apply that of Trionyx to the species which 



three nails to their feet. Witli such principles half have the marginal bony plates and a broad hind lobe 



the names introduced in Zoology or Botany might of the plastron, later writers have only introduced 



be changed. The new names proposed by Dumeril confusion in the nomenclature of this family bj' rc- 



and Bibron for Trionyx and Aspidonectes may them- versing his arrangement, which, according to tlu' law 



selves serve as an example. Now that it has become of priority, must in the end be adopted, in spite of 



necessary to subdivide into distinct genera the spe- every objection. The name Emyda, which is also 



cies which Dumeril and Bil)ron refer to Gymnopus, synonymous with Cryptojtus, Dum. and Bibr., apjjcars 



that name wouiil be inappropriate, according to their for the first time in Gray's Syn. Re])t., appended to 



own views, since all these new genera liave equally Griffith's Transl. of Ciivier's Regn. Anim., 1831. 

 naked feet ; and the genus Cycloderma of Peters ° Systcmatiseher Entwurf einer Anordnung der 



would render a change for Cryptopus necessary, as it Schildkroten, in Annalen des Wiener Museums, 



has retractile feet, like Cryptopus. 1836, 4to. 



' It may be said that Wagler ought to have re- ■• To these genera Fitzinger adds I'otamochelys 



taincd the name Trionyx for the species longest for Tr. javanicus, in Iiis Systema Rcptilium, published 



known ; but he undoubtedly had the right to name iu 1843. 



