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PROCEEDINGS OF THE NATIONAL MUSEUM. 



main features of either series can be predicted with some degree of 

 accuracy by a critical study of the opposing series. This is true 

 especially as regards the number, relative size, general form and pro- 

 portions of the principal cusps. 



To those who have studied tooth structure it is well known that 

 the trigonid of the lower molar bites on the inner side of the tooth 

 row and between or over the interspaces of the molars of the upper 

 series, in forms of the interlocking brachyodont type. The talonid, 

 when present, is opposed to the protocone of the corresponding upper 



Fig. 1.— Lowee cheek-teeth of Titanoides primaevus. Natural size. 



molar, and the development of the hypocone is always correlated 

 with and contingent upon the development, in the lower series, 

 either of the entoconid of the corresponding tooth or the paraconid 

 of the next tooth behind. Also the hypoconid bites into the middle 

 basin of the upper tooth crown between the paracone and the meta- 

 cone. 



Based on these known relations of cusps, I have attempted a con- 

 struction in clay of the upper series (see fig. 2, pi. 36) of the side cor- 

 responding to the lower teeth of the type (see fig. 1, pi. 36). The 

 details as worked out are of necessity largely conjectural and will 

 probably prove incorrect. I feel considerably more confident, how- 

 ever, regarding the main features. 



Thus constructed these upper teeth are decidedly titanotheroid in 

 general form and structure. The principal characteristics obtained 

 are: (1) The paracone and metacone are higher than the cusps of 

 the inner row and are selenodont in form; (2) to conform with the 

 two shallow basins of the lower molars, namely, the larger one of the 

 talonid, and the smaller and higher one of the trigonid, all the upper 

 molars have low, broad, conate protocones, and m * and m ^ small 

 but weU-defined hypocones; (3) p * and p ^ are wide and short, and 

 are composed of two main cusps, the outer (paracone) high and the 

 inner (protocone) low. If the lower premolar of the type is properly 

 identified as p^, the p^ above had probably not yet developed the 



