68 dr. j. e. gray on the trionychiDjE. [Jan. 7, 



A specimen in spirits, figured in the Cat. Sh. Rept. t. 30, received 

 from Utrecht, with the dorsal disk about six inches long, does not 

 show any indications of callosities, though it is quite as large as the 

 two dried specimens in the British Museum (one from the same col- 

 lection), which have these callosities well developed. This genus 

 seems peculiar in having the front margin of the thorax rounded 

 and its sides dilated so as partly to hide the feet when they are 

 withdrawn. 



A specimen from the Lao Mountains, collected by M. Mouhot 

 (59, 7, 8, 8), mentioned under Aspilus ornatus (Suppl. Cat. Sh. Rept. 

 p. J 03), evidently belongs to this species. 



Three young specimens from Ceram and Amboina have the callo- 

 sities not developed. The white spots on the head and the large 

 ones on the throat are so like those of larger specimens from Java in 

 spirits in the British Museum, that I think they will prove to be 

 only a younger state. 



There is a young specimen in the British Museum, obtained from 

 Mr. Bartlett, in spirits, the dorsal disk of which is pale brown, with 

 large scattered pale spots, with ridges of lines, which are separated 

 from one another, and larger in the hinder part of the disk. 



There is a bleached specimen in spirits received from the Leyden 

 Museum, which is very like a specimen figured in the ' Fauna Ja- 

 ponica.' Dorsal disk about six inches long and wide. It has no 

 indications of the sternal callosities ; and the form of the bones is 

 seen through the skin. I think it most likely belongs to this 

 species. 



There is a rather smaller bleached specimen in the Museum, in 

 spirits, received from Amboina. 



II. Emydiua. The hinder lateral edge of the sternum with flaps to 

 cover the hinder feet ; front pair of bones of the sternum with 

 callosities; the front odd bone of the dorsal disk united to 

 the ribs, and sometimes with a small free bone in the margin 

 before it. 



The similarity of the jaws and of the shape of the living Cyclan- 

 osteus which I had lately an opportunity of examining and figuring 

 from life (P. Z. S. 1870, t. 43), to the animal of Emyda, is so great 

 that I think they should be ranged in one group, and the family 

 which I called Emydidce, because the dorsal disk was armed with 

 bones, should be abolished. 



Some of the genera also have a rudimentary marginal bone in the 

 front of the disk, as in Emyda, which has also posterior marginal 

 bones. 



These animals have the odd bone in front of the back united to 

 the ribs in the adult age, so as to form a complete dorsal disk. The 

 genera Cyclanosteus, Emyda, and Heptathyra of the former family 

 have, in addition, a single bone in the centre of the front margin, 

 which is distinct from the front of the odd bone ; but the latter often 

 has a notch in the front margin to receive part of it. This bone, I 

 suppose, is a remnant of the marginal bones present in the other 



