VERTEBRATE FAUNA OP THE BLANCO BEDS. 61 



the external side of the crown. There are two or three accessory tuber- 

 cles at the anterior extremity of the crown closely appressed to the first 

 cross-crest. The lateral internal lobes of the trefoils are separated from 

 the single external lobe by deep grooves. 



Measurements o/M. S., 



Mm. 



Anteroposterior diameter 127 



Width at first crest at base 72 



Width at third crest at base 80 



Elevation of third crest 53 



The probable first true molar is unworn, and lacks the anterior border 

 and one-half of the anterior cross-crest. The tubercles composing the 

 crests are very distinct, are defined by deep vertical grooves, and con- 

 verge toward the median line with their apices. The cingulum passes 

 round the base of the second cross-crest, and between the crests is serrate, 

 and even pectinate. The principal cusp on one-half of the second and 

 third cross-crests is a little posterior in position to the crests of the oppo- 

 site side. 



Measurements of ?M. i. 



Mm, 



Anteroposterior diameter . . 98 



Width at middle cross-crest 59 



Elevation of middle cross-crest 47 



The supposed last premolar is still more complex than the first true 

 molar. The enamel layer is more grooved, forming plications on wear, 

 and the internal lobes of the trefoils of the external series are subdivided 

 so as to produce on wear from five to seven lobes. An external cingulum 

 is developed, which sends up strong tubercles at the valleys, but is weak 

 at the cross-crests. There are rudiments of a cingulum on the opposite 

 side. 



Measurements of ? P. m. i. 



Mm. 



Anteroposterior diameter of crown 78 



Width at middle of cross-crest 50 



Elevation of third cross-crest (little worn ) .35 



The only other North American elephants with double trefoils are the 

 Mastodon (JDibelodon) mirificus, Leidy, and the Tetrabelodon campester, 

 Cope. Both of these are fully tetralophodont, and belong to the older 

 Loup Fork fauna. The Dibelodon humboldtii, on the other hand, belongs 

 probably to a later fauna than the Blanco, viz. , the Pampean o'f South 

 America, which is more or less exactly equivalent to the Equus beds. It 

 would not surpise me if future research would show that the Blanco spe- 



