of ike Bones of the Sternum of Chelonians. 167 



larger roundish subhexagonal open space occupying the place 

 of the suture between the abdominal plates. 



Perhaps a somewhat similar structure exists in the young 

 Hydromedusa jiavilahris (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 Hydraspid^e, 

 as in the young Chelymys Victories 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 Bataguridse. 



Thus it will ap])ear that the tortoises that have a solid con- 

 tiimous sternum in their adult state have the bones of which 

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

 thougli they are all developed into a solid mass composed of 

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

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

 medusidie, CheJydra and Stauremys of Chelydrada3, Kachuga 

 (PL VJ. figs. 1 & 2), Morem'a, and Pangskura of Batagurid^e, 

 BMnoclemmys (PL V. fig. 4) of Emydidaj. 



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

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

 and the young of Notochelys platynota is like tliat of Batagur. 

 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 oi Kinosternon jyeiuisylvanicum 

 (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 

 Rhinoclenimys. ^ 



Mud- Tortoises (Trionyx). 



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

 Tortoises undergo little alteration of shape ; only the 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 wnth 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 



