Mr. Bell on the Box Tortois^. 299 



teeth of which have been figured in the above mentioned useful 

 work. 



Plate X, Fig. 5. Profile view of the jaws magaified. 



6. Lower jaw, natural size, left side, with the 



alveolar process removed, to exhibit the 

 roots of the teeth. 



7. Molarcsof the upper jaw, leftside, magaified. 



8. Molares of the lower jaw, left side, magaified. 



Art. XXXIV. A Monograph of the Tortoises having a 

 moveable Sternum, with Remarks on their Arrangement 

 and Affinities, ^y Thomas Bell, Esq. F.L.S. 



When, amongst a group of animals agreeing in their general 

 relatioDS, a number of species are found to differ from the rest in 

 some important character, and that character connected with an 

 essential difference in anatomical structure, we are justified in 

 considering those species as a distinct subordinate group, and, in a 

 systematic arrangement, in applying to it a distinctive appellation. 

 The subjects of the present memoir, were included amongst the 

 Emydes of Brongniart, and in their general appearance, as well as 

 in the structure of the different parts, they certainly have con- 

 siderable affinity with them. But the circumstance of their hav- 

 ing the sternum separated, as it were, into two or three divisions, 

 moveable upon each other, led Merrem to consider them as a 

 distinct genus, to which he applied the term Terrapene. Since 

 his work was published, Mr. Say, the excellent American Zoolo- 

 gist, who appears not to have seen Merrem's book, has, in a paper 

 on the freshwater and land Tortoises of the United States, also 

 formed them into a distinct group, with the generic appellation 

 Cisluda. As however the work of Merrem was published long 

 before Mr. Say's paper made its appearance, I have retained the 

 former name for one of the genera into which I have considered 

 it necessary to subdivide them. M. Spix has also applied the 



