EMYDA PUNCTATA, 
Os nuchale , in junioribus separatum, denique cum testa dorsali unitum. Sternum la¬ 
tum, planum, albidum, ex ossibus septem callosis constans; calli granulato-punctati; 
anteriores ovato-subreniformes ; impar rotundus; laterales irregulares, magni, ex- 
trorsum ad marginem dorsi attinentes; posteriores rhomboidei, in adultis conjuncti. 
Apertura posterior inter testam dorsalem et sternum, lobis binis coriaceis clausa. 
Mensura Corporis. 
ped. unc. lin. 
Longitudo totalis (collo porrecto). 1 2 4 
-corporis. 0 8 4 
Latitudo. 0 fi 5 
Longitudo sterni. 0 7 0 
Altitudo. 0 3 0 
The separation of the genus Emyda from the rest of the Trionychidce is too 
obviously natural to recpiire any laboured defence. It appears to have been 
made by Dr. Wagler and Mr. Gray about the same time, though the former 
has the advantage in priority of publication. Notwithstanding this, however, 
as Dr. Wagl er has applied the name of Trionyx to this genus, giving that of 
Aspiclonectes to the remainder of the family, I prefer retaining, with Mr. Gray, 
the name of Trionyx for the typical form, and giving a new appellation to the 
present genus, which must be considered as an abnormal form, and which 
consists of but one known species. 
The characters by which it is distinguished from all others of the Trionychidce 
are very striking. The osseous disk occupies, in the adult, almost the whole 
area of the back, reaching from the anterior margin nearly to the posterior, 
and entirely from one side to the other. The ribs are united through their 
whole length, before the animal has nearly attained his full size. The pos¬ 
terior margin is strengthened and supported by a series of bones unconnected 
with the disk: there are generally about 10 or 12 pairs, but several of them 
become united as the animal grows older. The sternum occupies a much more 
considerable space than in any other of the family; and the calli, which are 
seven in number, are of considerable size, almost touching each other. Another 
