NATURAL SCIENCES OF PHILADELPHIA. 23 



I. Tail elongate, five pairs of scuta of the plastron. 

 Two rows of marginal scuta ; inguinals separated from yentrals by a long 



scute. Macrochelys. 



One row of marginals ; inguinals as last. Ciielydra. 



II. Tail short, four pairs or fewer scuta of the plastron. 

 Anterior lobe of plastron fixed. Claudius. 



Anterior lobe of plastron movable on the remainder ? Stauremys. 



MACROCHELYS, Gray. 

 Gypochelys, Agassiz. 



MACROCHELYS LACERTINA, Schweigger. 



Ciielydra, Schw., Ciielydra temminckii, Troost., Chelonura, do., Hol- 



brook, Emysaurus, do., Dum. Bibr. 

 Mississippi River and rivers of Texas. 



CHELYDRA, Schw. 

 Chelonura, Flem. Emysaurus, Dum. Bror. 



CHELYDRA SERPENTINA, L. 



From Canada to Equador. 



This species presents an extraordinary range, enduring both 

 arctic cold and tropical heat. I can find no specific difference 

 between shells from Pennsylvania, Mexico, and Equador. Prof. 

 Peters has reached the same conclusion respecting Equadorian 

 specimens. 



CHELYDRA ROSSIGNONII, Bocourt. 



Miss. Sclentif. Mexique Reptiles et Batrach, 1870, p. 18, Tab. V., fig. 2. 



This species differs from the last in having four barbels instead 

 of two, a larger plastron with a stouter bridge, and in the stronger 

 and longer dentations of the posterior margin of the carapace. 



Mexico and Guatemala (Bocourt). 



Some extinct species of this genus have been discovered in the 

 miocenes of Europe. 



CLAUDIUS, Cope. 



Proceed. Ac. Nat. Sci. Phila., 1865, 1867. Bocourt, Miss. Sei. Mex. 

 Rept., p. 19. 



This genus has received several accessions through the efforts 

 of those excellent naturalists, MM. Sumichrast and Bocourt. 

 The latter has described two species as previously named, but I 

 3872.] 



