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to the idea that they belonged to animals of the same genus, were it 

 not that the teeth present modifications of form in the Scelidothere, 

 as distinct from those of the Mylodon as are any of the minor dental 

 differences on which genera or subgenera of existing Mammalia are 

 founded in the present state of zoological classification. 



487. An upper molar tooth of the Scelidotherium leptocephalum. 



488. A section removed from the right ramus of the lower jaw of the Scelido- 



therium leptocephalum, showing the forms of the four molar teeth in 

 transverse section. 



The first molar is not divided by a disproportionate interspace from 

 the rest: its transverse section gives a narrow inequilateral triangle, 

 with rounded angles, and the base turned inwards and obliquely for- 

 wards. The second molar also, instead of an elliptical transverse sec- 

 tion, presents a triangular one with the angles rounded off, and two of 

 the sides slightly indented ; it resembles the antepenultimate molar in 

 the Mylodon rohustus. The third and fourth molars of the Scelidothere 

 are more compressed than in the Mylodon ; the bony axis of their 

 transverse section is from before backwards, instead of transversely. 

 The fifth molar has a trihedral form, with the broadest side turned 

 outwards and slightly indented. 



In the lower jaw of the Scelidothere the differences in the form of the 

 teeth from those in the Megatherium, Megalonyx and Mylodon, are 

 equally manifest, especially in the prismatic form of the first molar : the 

 last molar resembles that of the Mylodon Darwinii ; the grinding sur- 

 face of this tooth being divided into two lobes by two oblique channels 

 which traverse longitudinally, one the outer, the other the inner side of 

 the tooth : but these are shallower than in the Mylodon Darwinii, and 

 the lobes are more equal and more flattened. The two middle teeth differ 

 more markedly from the corresponding ones in any of the species of 

 Mylodon : the transverse section of both these teeth presents, in the 

 Scelidothere, a compressed oval form, with the large end turned obliquely 

 forwards towards the outer side of the jaw, and slightly indented, whilst 



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