322 On the Bones of the Sternum of young Tortoises. 



and Trachemys of the family Pseudemydaa (which are confined 

 to America), and Kachuga of the family Bataguridas (which are 

 confined to Asia, and have the internal lobes of the sternal 

 bones in the young specimens broader than in any of the pre- 

 ceding genera). In all the above genera the lobe of the in- 

 ternal edge of the anal pair of bones is near the anal end of 

 that bone, except in the genera Pseudemys and Batagur, where 

 it is much nearer the fore end of the internal edge, leaving 

 a broad vacant space, so that very young specimens appear 

 to have three vacant spaces behind the hinder edge of the 

 front pair of lateral bones. 



The bones of the sternum of the young Platysternon are 

 intermediate in form between these and the next division ; 

 that is to say, the front and hinder lateral bones are dilated 

 into a triangle, dentated on the inner edge, and the anal pair 

 have a broad lobe on the front part of the inner edge, as in 

 Kachuga and Pseudemys. 



III. The third form differs from the second in the lateral 

 pairs of bones and the anal bones of the young specimens being 

 dilated, ovate or triangular, leaving a space on each side of 

 the odd bone, a large, more or less rhombic, space between 

 the front and hinder lateral pairs, and a smaller rhombic 

 space between the hinder edge of the hinder lateral pair and 

 the front edge of the anal pair — as in Lutremys and Cuora 

 (fig. 14) (both from the Old World) in the Cistudinidaj, and 

 Malaclemmys (from North America) in the Malaclemmyda?. 

 The young Pelomedusa 1 the type of the African family Pelo- 

 medusidffi, among the Pleuroderes, has the sternum very like 

 that of Malaclemmys. 



IV. The fourth form, which appears to be peculiar to the 

 family Chelydrada3, has the four pairs of bones of which it is 

 composed more or less dilated, leaving in the very young state 

 an elongate central vacant space, which is generally pervaded 

 in front by a very long slender odd bone ; this bone is entirely 

 wanting in the most developed types of the family called the 

 Trap Tortoises, as the genera Kinosternon and Sicanka. Un- 

 fortunately I have not been able to examine the sterna of 

 several genera of this group : indeed I have only been able to 

 see the sternum in a small well-developed specimen of Kino- 

 sternon. A very young specimen of Swanka has never oc- 

 curred to me ; and I am not aware that it has ever been seen 

 or described by any American or other zoologist. I have 

 figured the outside of the sternum of a very young Kinosternon 

 pennsylvanicum in my former paper (' Annals,' 1873, xi. pi. 5. 

 fig. 6). 



