of the Bones of the Sternum of Chelonians. 165 



In Chelydra serpentina^ even when the shell reaches 7 inches 

 length, the sternum is not united along the central longi- 

 tudinal suture, and there is a triangular cavity on each side 

 of the narrow lanceolate odd bone and the front end of the 

 front lateral, and a moderate-sized square unossified portion 

 between the inner ends of the front and hinder lateral bones on 

 the suture between the pectoral and abdominal plates. 



The sternum of the skeleton of the young Stauremys Salvinii 

 in the British Museum is like that of Ghelydra ; but the inner 

 edge of the front bones is further apart, and the odd sword- 

 shaped bone is thinner and longer. 



II. In the second form the four pairs of bones form a ring 

 round the margin of the sternum, the two pairs of lateral bones 

 being the least developed and forming the narrowest part of 

 the ring, leaving a large open space in the centre between all 

 the bones which form the greater part of the sternum, with 

 the ])oiut of the odd bone projecting into it. This form is well 

 seen in the sternum of Cyclemys dhor (figs. 3), belonging to 

 the family Cistudinid^. 



Rhinoclemmys scabrd (fig. 4). As this animal grows, the 

 front part of tlie sternum becomes more dilated and extended 

 externally on the front of the outer side. It is also to be ob- 

 served in the animal that I have described and figured as Emys 

 pidclierrima (Cat. Sh. Kept. pi. xxv. fig. 1), which may be a 

 I\h{)wclemmys. These two latter terrapins belong to the 

 family Emydidffi. 



III. This form is somewhat intermediate between the two 

 former. The four pairs of bones in the young animal are even 

 less developed, and form only a narrow ring round the margin 

 of the sternum, leaving a very large part of the sternum only 

 formed of membrane, occupying more of its space than even 

 in the former kind ; but the anterior lateral and posterior 

 lateral bones throw out each a more or less narrow bony pro- 

 cess across the space, dividing it into three portions. Into the 

 front edge of the front one the small triangular odd bone pro- 

 jects. In Notochelys 2)latynota (PL IV. fig. 5) the fi'ont pair 

 of bones is moderate. The inner process of the front pair of 

 lateral bones is small, but broad and divided into three or 

 four finger-like lobes at the end. This belongs to the family 

 Cistudinidai. 



In Kachuga (PI. VI.) the front pair of bones is less deve- 

 loped. The inner lobes of the front lateral pair of bones are, 

 as in the former, broader and divided into finger-like lobes at 

 the end. The internal bony lobes of tlie hinder lateral bones 

 are well developed, and like those of the front pair of bones, 

 but much narrower ; but, unlike the sternum of Notochelys 



