TORTOISES. 45 



The Tracaxa. Peltocephalus Tracaxa, Dum. et Bib. E. G. 

 ii. 378, t. 18,/- 2. Emys T. Spix, Braz. 6, t. 5. Wagler, Syst. 

 135. Emys macrocephala, Spix. Braz. 5, t. 4, (young). 



Shell ovate, subsemicylindrical, smooth, entire, blackish brown. 



a. Adult, stuffed. S. America. 



10. Podocnemis, Wagler. 



Head rather depressed, covered with flat shields, with a deep 

 groove on the forehead. Chin 2-bearded. Jaws naked, slightly 

 arched, toothless. Legs broadly webbed, the hinder with two broad 

 thin scales at each claw. Tail short, not clawed. Shell rather 

 solid. Nuchal plate none. Sternum broad, not mobile. 



The Broad Podocnemis. Podocnemis expansa, Wagler, Syst. 

 135, t. 4,/. 1—31. Dum. et Bib. E. Gen. ii. 283, t. 19,/. 1. Emys 

 Amazonica, Spix, Braz. i. t. 1, 2,/. 1, 2. Schiocig. Prod. 299, 

 n. 8. Schlegel, F. Jap. 48. Gray, Syn. R.41. Test. Arrace, Hurnb. 

 Pers. Nar. iv. 482 ? 



Shell oval, entire, keelless, very depressed when adult, tecti- 

 form when young, much and horizontally expanded over the hind 

 legs. 



Inhab. Cayenne. Mus. Paris. 



The Cayenne Podocnemis. Podocnemis Duraeriliana, Wag- 

 ler, Syst. 135. Dum. et Bib. E. G. ii. 387. Emys Duraeriliana, 

 Schweig. Prod. 300, n. 9. Schlegel, F. Jap. 48. Gray, Syn. 42. E. 

 Cayennensis, Schweig. Prod. 298, n. 6, (young). E. erythroce- 

 phala, Spix, Bras. t. 7, (young). 



Shell oval, convex, swollen, nicked in front, brown, varied with 

 black ; the second and third vertebral plate keeled ; sternum yel- 

 lowish, under side of marginal plates with a black spot. 



Inhab. Brazils. Mus. Paris. 



There is in the British Museum a fossil species of this family 

 from Sheppey, peculiar for having a flat sternum, round at each 

 end, and having the sterno-costal suture covered with several ad- 

 ditional plates (like Platysternon amongst the Emydidai). I have 

 long since named it after my excellent friend and former superior, 

 and now colleague, Megasternon Kwnigii. 



