in the Sternum of youny Tortoises. 321 



are furnished on the inner side with a lobe directed towards the 

 centre of the sternum and torn at the end. The hinder lateral 

 pair have a small conical prominence on the middle of the inner 

 side : indeed they are very like those of Notochelys platynota ; 

 but the lobe on the inner side is much smaller and less marked. 

 The young sternum of this species is intermediate between the 

 form that is found in Geoemyda spinosa and that which is 

 common to the species of Emys. 



The sterna of the young specimens of BelUa (fig. 10) and 

 Damonia (figs. 11 & 12) are much thicker and more solid 

 than the sterna of the young of Malaclemmys^ Pseiidemys 

 (fig. 9), Chrysemys (fig. 7), and Trachemys (fig. 8) of America, 

 and Emys (fig. 6), Emmenia (fig. 5), and Platystenion (fig. V6) 

 of Europe and Asia. The skin that fills up the vacancies 

 between the bones is much thicker, and so opaque when dried, 

 that the sterna might be regarded as solid ; but the cavities 

 leave a sunken space visible on the outside, and they are easily 

 pierced with a pin, showing that there is only a dried carti- 

 laginous skin, though so thick and opaque that it looks like 

 bone. 



The development of the bones, and the changes in form 

 which they undergo, in the Freshwater Turtles or Steganopodes 

 may be arranged under four heads. 



I. In the more terrestrial animals the bones of the sternum in 

 the young specimens are narrow, and form a marginal ring 

 round the circumference of the sternum, leaving a large oblong 

 central unossified space, which eventually becomes filled up, as 

 in the genera Cyclemys in the Cistudinidaj, and Geoemyda and 

 Rhinoclemmys in the Emydse. 



The sternum of the young Geoemyda grandts (fig. 4) has 

 rudimentary lobes diverging from the inner side of the anterior 

 and posterior lateral bones, forming a passage to the next 

 form ; but this may be the way in which the central space is 

 filled up, and is only a matter of growth. 



II. In the genera which have the second form all the bones 

 of the circumference of the sternum are broader, and the front 

 and hinder lateral pairs and the anal pair have a more or less 

 broad lobe on the inner side, tending towards the central 

 suture, dividing the central space into three parts : the front 

 one is generally the smallest, and divided in the middle by the 

 central odd bone, the middle one the largest and broadest, 

 and the hinder one smaller and generally longer than broad. 

 These processes enlarge, and unite and solidify in the sternum — 

 as in Notochelys of the Cistudinidaj, in Chrysemys of America, 

 Emys and Emmia of the ]\leditcrranean region, BelUa and 

 Damo)ua (from Asia) of the family Malaclcmmydai, Pseudemys 



