VERTEBRATE FAUNA OF THE BLANCO BEDS. 



63 



various species of Tetrabelodon, but the last inferior molar has five well 

 developed cross-crests and a prominent heel and one more cross-crest than 

 any of the species cited, thus resembling the tetralophodont forms of 

 both genera. I would have suspected that this species is tetralophodont 

 had I possessed only the last molars, but the presence of the second true 

 molar in both rami in excellent preservation shows that this is not the 

 case. It agrees in the characters of its molars very closely with the typi- 

 cal specimen of the species from Michoacan, Mexico, described and figured 

 by Von Meyer as above cited. The last true molars are not fully pro- 

 truded, and the inference to be derived from the character of the second 

 molars is that that tooth would have but four crests and a keel. On this 

 supposition I suspected the animal to represent a species distinct from 

 the M. tropicus and named it M. successor, as above cited. This name is 

 now withdrawn. 



In the inferior molars the apices of the crests are very obtuse. The 

 external half of each cross-crest possesses a single accessory tubercle on 

 each side of its internal extremity, which, together, produce the trefoil 

 section on wear. The internal halves of the crests possess no accessory 

 tubercles except on the first cross-crest, where they are present, and a 

 trace at the posterior base of the second. Each half is divided at the 

 summit and on the sides by a groove, into two lobes, which are only 

 superficially distinguished, and more plainly in the anterior than in the 

 posterior teeth. There are no cingula, but there are tubercles at the 

 mouths of the external valleys. 



The last inferior molars support, as above remarked, five cross-crests 

 and a well developed heel of two tubercles. In the last two cross-crests 

 the internal halves are situated a little in advance of the external halves. 

 The general outline of the crown is that of an elongate wedge. The 

 principal lobes of the fifth cross-crest converge upward, but the con- 

 vergence is less than in the others. 



The second molars are well worn, but not so as to obliterate the pattern 

 at any point. On the external side the valleys remain open, but on the 

 internal side the adjacent enamel borders of the crest are in contact so as 

 to obliterate the valleys. The bilobate character of the external half of 

 each crest is well preserved. There is a rudimental cross-crest behind 

 the third, in close contact with it, which does not extend across the 

 crown, and which is less developed than in the D. liumboldtii. The 

 enamel in both true molars is smooth, excepting some horizontal wrinkles 

 on the ends of the cross-crests. 



The symphysis is short and abruptly acuminate and slightly decurved 

 at the apex. Its length is less than that of the second molar tooth, hav- 

 ing shorter proportions than in the corresponding part in D. liumboldtii, 

 and very much shorter than in D. cordillerarum, as represented by Bur- 

 meister. 



