of the Bones of the Sternum of Chelonians. 167 



larger roundish subliexagonal open space occupying the place 

 of the suture between the abdominal plates. 



Perhaps a somewhat similar structure exists in the young 

 liydromedusa flavilahris (PL VI. fig. 3) ; but I have only been 

 able to examine and figure the outside of this specimen, and 

 have not described the separate bones of which it is composed. 

 But this form does not seem to be universal in the Hydraspidse, 

 as in the young Chelyinys Victorice in the British Museum 

 (about five inches long), examined from the outside, there is a 

 narrow rhombic unossified space in the suture between the pair 

 of abdominal plates, and a narrower lanceolate space between 

 the hinder part of the preanal plates, somewhat like what we 

 find in the young Bataguridas. 



Thus it will appear that the tortoises that have a solid con- 

 tinuous sternum in their adult state have the bones of which 

 it is composed of a very different form in their young state, 

 though they are all developed into a solid mass composed of 

 nine bones in the adult state, as, for example, Malaclemmys 

 (PI. V. fig. 1) of Malaclemmydge, Pelomedusa (fig. 2) of Pelo- 

 medusida3, CheJydra and Stauremys of Chelydradas, Kachuga 

 (PI. VJ. figs. 1 & 2), Morenia, and Pangshura of Bataguridee, 

 RMnoclemmys (PL V. fig. 4) of EmydidaB. 



Thus, among the Box Tortoises, the sternum of the young 

 Cyclemys dhor (Pl.V. fig. 3) is very like that oi Uhinodemmys^ 

 and the young of Notochelys inlafynota is like that of Batagar. 

 We have not had the opportunity of examining the young 

 state of the other genera of Box Tortoises. 



I labour under the same disadvantage with regard to the 

 young state of the two-flapped Trap Tortoises. I have only 

 seen the young stuffed specimen oiKinosternoniyennsylvanicum 

 (PL V. fig. 6) , which I can only examine from the outside. That 

 has an oblong slender unossified space occupying more than 

 half the length of the central suture of the sternum, somewhat 

 like, but narrower than, the unossified space of Cyclemys and 

 lihinoclemmys. 



Mud- Tortoises (Trionyx) . 



The bones of the sternum of the young and adult jMud- 

 Tortoises undergo little alteration of shape ; only tlie adult 

 animals have on the outer surface of each an expanded bony 

 callosity, which, like those on the outer surface of the ribs, 

 is pitted externally and covered with a soft skin, so that the 

 expansions of the ribs and sternal bones are only seen in the 

 animal when it is dry. They are peculiar for having the first 

 pair of sternal bones elongate and bent like an L, one branch 

 of each being directed straight forward, and the elongate 



