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25 



MASTODON 



appears not so distinct as in the other teeth. The lobes of each transverse 

 pair conjoin through a medial tubercular offset springing from each lobe, and 

 though the offset to the second inner lobe is not evident in the left tooth 

 figured, it is distinct in the right tooth. The first outer lobe of the tooth is 

 the largest, and independent of. its medial tubercular offset is simply conical. 

 The contiguous inner lobe is more extended fore and aft, and independent of 

 its medial offset is divided into a row of four eminences, which decline forward 

 and are thence continued in a tuberculated ridge curving in advance of the 

 outer lobe. Of the posterior pair of lobes the outer is the larger and the 

 simpler, while the inner, the smallest of the crown, independent of its medial 

 offset, is divided into three eminences, and is continued behind by a tuber- 

 culated ridge to the base of the contiguous outer lobe. 



In the right tooth the inner lobes are less developed, less distinct from 

 each other, and together appear more as a strongly tuberculated ridge em- 

 bracing the inner semicircumference of the crown. 



The measurements of the first premolar are as follows : 



Right tooth. Left tooth. 



Fore and aft diameter of the crown . . 36 mm. 37 mm. 



Greatest width transversely . . . 30-5" 32 " 



Depth at the first outer lobe ... 24. 5 " 



The crown of the second upper premolar, plate vi. figs. 3 and 4, is quad- 

 rate, fore and aft widest outwardly, and transversely widest opposite the 

 anterior lobes. The constituent lobes partake of the character of those of the 

 back molar teeth. As in the first premolar, the anterior lobes are the largest 

 and the postero-internal lobe is the smallest. Deep notches separate the 

 anterior from the posterior lobes, and a less deep notch separates the anterior 

 pair. The antero-internal lobe forms a tubercular ridge, extending from the 

 lobe behind and curving outwardly in advance of the position of the antero- 

 external lobe. The summits of the anterior lobes are divided into three and 

 four eminences. The posterior lobes together form a transverse ridge, sub- 

 divided into half a dozen eminences. They are conjoined behind by a ridge, 

 and together enclose a considerable pit. The deep transverse valley of the 

 crown exhibits a conspicuous central tubercle. 



The measurements of the tooth are as follows : 



Fore and aft diameter of the crown ..... 45 mm. 

 Transverse diameter at base of the anterior lobes . . 41 " 



Transverse diameter at base of the posterior lobes . . 35 " 



