Cope.] ' 4bU [Nov. 15, 



Measurements of Superior Molars. mm. 



Diameters of m.i{^°^^^«P«^terior 20 



t. transverse 15 



i longitudinal 83 



Diameters of m. ii -l anteroposterior 30 



( transverse 15 



Long (oblique) diameter of m. iii 33 



" " *' " m. iv 31 



Diameter do. at right angles to the longest 17 



! longitudinal 70 

 anteroposterior 30 

 transverse (longest) 25 



Mylodon renidens Cope, sp. nov. 



This species is founded on a right maxillary bone, which contains all 

 but the first molar tooth. This tooth is represented by an alveolus broken 

 anteriorly, and the free portions of the crowns of the second and third 

 molars are broken off. The crowns of the fourth and fifth molars are 

 perfect. Associated with this specimen are the following, which probably 

 belong to the same species: The posterior three molar teeth of the Inferior 

 series; a superior first molar in place in the anterior part of a right maxil- 

 lary bone. 



The superior and inferior series referred to are considerably smaller 

 than the corresponding parts of the M. harlanii, and might be supposed 

 to have belonged to young Individuals. As these animals are, however, 

 monophyodont, it is evident that the only way in which a permanent 

 dentition could be adapted to a growing jaw is by the appearance of but a 

 part of the dentition at a time, or by a conical form of tooth crown, which 

 will permit of the expansion of each tooth at the base. This mode of 

 enlargement does exist for a short time among the Bruta, and this is 

 exhibited in the teeth of the species called Sphenodon by Lund, and 

 Megalonyx sphenodon * by myself. The wider base is visible in the inferior 

 series of Mylodon renidens in this collection, but the largest dimensions 

 thus obtained are much below those of the M. harlanii. The superior 

 molars display little If any expansion at the basis of the roots. The 

 crowns of both superior and inferior molars are worn. The presence of 

 a third inferior molar of a species of much larger size, but of the same pe- 

 culiar character as that of the smaller series, sliows that the character 

 is constant and significant. 



The typical specimen consists of almost the entire right maxillary bone, 

 with the teeth in place as above described. The alveolus for the first 

 molar indicates that the latter has a subcylindric shaft, curved slightly 

 posteriorly at the extremities. The second molar has a rather narrowly 

 oval section, with a very slight concavity on the inner side, tlie long axis 



* Proceeds. Amcr. Philos. Soc, 1871, p. 83. 



