Dr. J. E. Gray on Chelonians. 301 



gical Society's Gardens, and Avere described as Emyst Ben- 

 nettii. The underside is white, with large solid black spots. 



KiNOSTERNON. 



The pelvis very large, the hinder rami long, cylindrical. 

 The anterior part broad and concave in front, as in Sioanka. 



The skeleton of Staurotypus is very like that of Kinosternon 

 and Swanka. 



SWANKA. 



The sternum of almost all the specimens is flat or slightly 

 convex ; but in one specimen (g) in the British Museum, which 

 has rather a large head, the sternum is very flat in front and 

 concave, especially over the hinder cross suture. 



Sioanka scorpioides. 



The specimens appear to differ in the development and length 

 of the tail, and in the strength of the spine at the end of it, 

 which is strongest in the longest-tailed. These are said to be 

 sexual differences ; but there is no difference in the form of 

 the sternum, or of the caudal marginal plates, between the 

 long- and short-tailed specimens. 



The three-keeled Swanka scorpioides generally has the 

 caudal end of the sternum entire and rounded ; the single- 

 keeled S. macxdata has this part truncated or notched, as is 

 also the case in S.fasciata^ of which only a single specimen 

 has been observed. 



The anterior lobes of the sternum covered by the postgular 

 and pectoral plates united into one bone, with a straight suture. 

 The abdominal plates cover four four-sided bones. The pre- 

 anal and anal plates cover the hinder mobile flap, which con- 

 sists of a pair of bones separated by a central suture. 



The pelvis has very long, slender lateral bones to the ver- 

 tebree ; the front of the pelvis is very peculiar, having a large 

 concavity occupying nearly the whole of its surface in front. 



The hinder toes are scarcely longer than the front ones. 



Hydromedusa. 

 This genus may be divided into two subgenera. 



I. Hydromedusa. 



The head rather large, back of neck smooth. Front pair of 

 marginal plates four-sided, broader than long ; the front ver- 

 tebral plate oblong, transverse, as broad as the front marginal 

 plates, Avith truncated sides ; the two hinder vertebral and 



