60 GKOLOGiCAL SURVEY OF *EXA^. 



DTBELODOTSr, Cope. 



Proceeds. Amer. Pliilos. Soc, 1884, p, 2; American Naturalist, 1889, 

 p. 193. 



DIBELODON HUMBOLDTII, Cuvicr. 



Plates XV, Figures 2-4; XVI, Figure 4, 



Cope, Proceeds. Amer. Philos. Soc, 1884, p. 5. 



Mastodon humboldtii, Cuvier, Ann. de Museum, VIII, 1896, p. 413; De 

 Blainville, Osteographie, Gravigrades; Gervais in Castelnau's Voyage en 

 Amerique du Sud; Burmeister, Annales du Museum de Buenos Ayres. 



The palate, with the penultimate superior molars of this mastodon, were 

 found by myself, buried with a number of bones of the skeleton. Mr. 

 W. F. Cummins found in two other localities two molars, probably the 

 last premolar and first true molar of one individual, and a last premolar 

 of another individual. No entire last true molar, no symphysis mandi- 

 buli, and no tusks were found. It follows that the identification of this 

 species is not as definite as is to be desired; nevertheless I can find no 

 important difference between the teeth obtained and the corresponding 

 ones of D. humboldtii. 



The penultimate molars of the Z>. humboldtii are figured by De Blain- 

 ville and the (?) first true molar by Burmeister. The last molars are fig- 

 ured by all the authors above quoted, and I have a perfect specimen in 

 the entire ramus with symphysis in my private collection from Buenos 

 Ayres. The only character in which the Blanco molars differ from those 

 figured and described as above mentioned, is the larger size of the heel, 

 which forms a small fourth cross-crest on continued wear. It consists of 

 three cusps, two on one side of the middle line and one on the other, 

 whose combined section is crescentic, with the concavity backwards. Its 

 transverse extent is about half that of the true crests. A distinct rudi- 

 ment of this structure is represented as existing in the D. humboldtii of 

 South America. The Blanco teeth can not, however, be regarded as 

 tetralophodont. 



This species is readily distinguished from all other American trilopho- 

 dont species by the similarity in composition of the internal and external 

 halves of the molar crests. Both have lateral internal tubercles, so that 

 both wear into similar trefoils. The marginal portions of these trefoils 

 are equidistant on the opposite sides of the crown, so that they do not 

 come into contact on wear, while the two inner lobes of the trefoils come 

 into contact on wear, and completely block the transverse valleys. There 

 are robust but low cingular tubercles between the crests on the internal 

 side at the base of the crown, but these are not connected with each other, 

 so that there is no cingulum. There are no corresponding tubercles on 



