272 HAY—EXISTING GENERA OF THE TRIONYCHIDA. [Oct. 2, 
Platypeltis, Trionyx sinensis as the type of Pe/odtscus, and T. sub- 
planus as the type of Gray’s Dogania. Dr. Baur also recognized as 
valid genera Cyc/loderma Peters, with its type C. frenatum; Cycla- 
norbis Gray, with the type Crvyptopus senegalensis; Isola Gray, with 
the type Zrionyx leithit ; Chitra Gray, with the type Zrionyx indt- 
cus, and Pelochelys, with the type P. cantorit. 
Leaving out of consideration the genera Pelochelys, Chitra, 
Cycloderma and Cyclanorbis, as being valid, and likewise invulner- 
able on other grounds, as well as the various genera founded since 
1846, and cited by Boulenger as synonyms of his 77/onyx, let us 
consider the content and value of the others. 
In his classification of the Trionychide, Dr. Baur gave great 
weight to the amount of reduction of the posterior nares by the 
inner and posterior extension of the maxilla. To the present 
writer this character seems to be of little value. The two con- 
ditions of being ‘‘reduced’’ and of being ‘‘not reduced’’ can 
hardly be defined, and they are probably connected by every grada- 
tion. It is solely on this character, so far as we know, that he 
has separated generically his Pelodiscus agassizit and Platypeltis 
ferox (Amer. Naturalist, xxii, p. 1121; Proc. AMER. PHILOs. 
SOC: ,) XXXL, Pp. 277). 
Trionyx, with Zestudo granosa as type, must be regarded asa 
valid genus. 
Aspidonectes Wagler, restricted by Bonaparte, 1836, and Fitz- 
inger, 1843, with Zestudo triunguis Forsk. as type, must be applied. 
to the group designated by Boulenger I, B, 3 (Cat. Chelonians, 
p- 245), and to that included by Baur (Proc. AMER. PHILOs. Soc., 
xxxi, p. 220) under the name Pedodiscus, with the exception of his 
P. agassizit. In the same genus the present writer would include 
Boulenger’s group I, B, 2, containing the species cartilagineus, for- 
mosus and phayret. These were placed by Baur in the genus Asfi- 
donectes, as this was limited by him; but did the group form a 
genus distinct from that whose type is Zestudo triunguts, it ought to 
be called Potamochelys ; since, as already stated, Fitzinger in 1843 
made the species cartilagineus (javanicus) the type of this genus. 
This group differs from the preceding only in having ‘‘ the alveolar 
surface of the lower jaw with a strong longitudinal symphysia] 
ridge,’’ a character which appears to the writer as insufficient. In 
the same genus must be placed Z7ionyx subplanus Geoffr. As 
