FREE INSTITUTE OF SCIENCE 



MASTODON ^ 



from their general appearance of age and other conditions, are so correlated as 

 to render it probable that they belonged to the same animal, an individual of 

 adult age. The teeth consist of the series of upper true molars of the right 

 side, and those of the left side except the last one. The crown of the right 

 second true molar is broken away at its back part, but that of the conespond- 

 ing left tooth is complete. The crown of the last molar is also complete, and 

 those of the first molars nearly so. The latter are well worn, but the last 

 molars had just commenced to .protrude, and in the specimen preserved is 

 only slightly abraded from use on the summit of the first outer lobe. 



The first molars, represented in plate ii. figs, i and 2, differ a little in size 

 and the condition of wear, the left being slightly the larger. The constituent 

 lobes of the crown are worn away nearly to their bases, the inner ones to the 

 greatest extent. The exposed dentinal areas are strongly depressed, the 

 broader ones of the inner lobes even to a greater depth than the bottom of the 

 valleys of the tooth. 



In the right tooth the dentinal areas of the anterior pair of lobes con- 

 join by a narrow isthmus, in the middle lobes are separated by a little neck, 

 but in the posterior lobes are still separated by a double wall of enamel. In 

 the left tooth the worn condition in a manner seems reversed ; in the anterior 

 lobes the dentinal areas being separated as in the posterior lobes of the former 

 tooth ; in the middle lobes they are united by a narrow isthmus, and in the 

 posterior lobes are completely united, leaving only an enamel islet as a rem- 

 nant of the original separation. Contrary to the usual course of wear of the 

 teeth of the Mastodon, these look more worn behind than in front. 



The measurements of the two teeth are as follows : 



Fore and aft diameter of the crown 

 Transverse diameter at base of anterior lobes 

 Transverse diameter at base of posterior lobes 



The second true molars, of which the left one is represented in plate i. 

 fig. 2, are typical of the molar teeth in general of the species. Conforming to 

 the first molars, their crown is composed of three pairs of lobes springing from 

 an expanded base and embraced by a tubercular basal ridge. The inner lobes 

 are closely united through their contiguous buttresses, which completely 

 divided the transverse valleys of the crown. The anterior buttress of the 

 first inner lobe is prolonged in the usual manner by an equally stout ridge 

 extending in advance of the contiguous outer lobe. There is no buttress to 



