16 CHELONIA. 



PYXIDEA, Gray. 



Thorax and sternum solid, entirely bony; sternum without transverse 

 joint ; a cartilaginous longitudinal suture between sternum and upper shell. 

 Upper shell angular ; sternum flat ; the suture between the pectoral and 

 abdominal plates straight. Legs with transverse shield-like scales above; 

 toes scarcely webbed. 



Only one species is known. 



Pyxidea mouhotii. (Plate lY. fig. D.) 



Cyclemys mouhotii, Gray in Ann. ^- Mag. Nat. Hist. 1862, x. p. 157. 

 Pyxidea mouhotii, Gray, MS. 



Form. — Shell moderately elevated, with three strong longitudinal ridges; the space 

 between the ridges rather flat. The anterior and posterior margins serrated, the latter much 

 more deeply than the former. The median ridge commences behind the nuchal and termi- 

 nates before the caudals, and is nearly equally strong throughout its course. The lateral 

 ridge runs over all the costals, much nearer to the vertebral line than to the lateral margin 

 of the shell. The sternum is nearly twice as long as broad, rather narrower between the 

 pectoral incisions than between the inguinal, truncated in front and deeply notched behind ; 

 it is very slightly concave in males. 



Plates. — Nuchal plate much longer than broad, sometimes absent; the three middle 

 vertebral plates much broader than long, the last much broader than the caudals, each of 

 Avhich terminates in a point, the two points being separated by a deep notch. Gulars sub- 

 quadrangular, rather broader than long ; the suture between them shorter than that between 

 the postgulars. Pectorals shortei- than postgulars and abdominals. Prteanals of about the 

 same size as the postgulars ; the suture between the prsanals is shorter than that between the 

 anals, which are comparatively large, and the posterior margins of which meet at a rather 

 obtuse angle. 



Jaws not denticulated. Front part of the fore limb and sole of the hind limb covered with 

 large, thin, imbricate scales. Tail shorter than the head. The shell is yello-wish, more 

 brown on the lateral parts. 



Seven specimens were collected by the lamented Mouhot during an expedition in the Lao 

 Mountains in Cochinchina, where he unfortunately perished. The species does not alter 

 much with age, the shells of the difiierent individuals being from 3 to 7 inches long. 



In a half-grown specimen the anterior lobe of the sternum appears to be slightly moveable, 

 whilst it is entirely immoveable in the larger specimens. 



The figm-e represents one of the typical specimens, of tlie natural size. 



