SUPERFAMILY^ MASTODONTOIDEA 329 



is preoccupied b}'- Warren for M. latidens, M. arvernensis, etcetera, and 

 therefore can not be used. 



^ Parallelism 



Again it is said that there are transitions between certain of these 

 phyla; for example, between the longirostrines and the brevirostrines in 

 the Pliocene of Europe. Such transitions may be observed in single 

 structures, because the law of pa/rallel evolution is constantly at work; for 

 example, in the family Bunomastodontidse there are at least four clearly 

 distinct phyla, which we may at present separate as the longirostrines, the 

 rhynchorostrines, the South American brevirostrines (M. andium, M. 

 humholdtii) , and the American Trilophodon serridens phylum (unnamed 

 at present). All these animals are united by the common possession of 

 the bunomastodont type of molars, composed of compressed inner and 

 outer lobes, to which Cuvier applied the original term "mastodon," be- 

 tween which sprang up also single bunoid intermediate cones forming 

 trefoils (Phiomia, Trilophodon) , then gradually both internal and ex- 

 ternal trefoils, such as are found in the long-jawed M. campester and M. 

 longirostris and independently arise in the short-jawed M. humholdtii. 

 Thus the internal and external pairs of trefoils develop by parallelism in 

 four separate lines of descent in the phyla belonging in the new family of 

 Bunomastodontidas (Osborn, 1921. 514), the ph3da being united by this 

 common family character as well as by the presence of a broad enamel 

 band on the superior incisor teeth. They are still more clearly separated 

 from each other by the elongation or by the abbreviation of the jaw or by 

 the formation of a down turned or beaked jaw. 



Tt is by this interpretation of the facts of descent, and by the exclusion 

 of parallelism, and not by theory that we reach the polyphyletic sul)- 

 division of the Mastodontoidea, as follows : 



Superfamily, Mastodontoidea 

 Family, Mastodontid^ Family, Bunomastodontid.e 



(Grinding teeth lophodont, no inter- Grinders bunomastodont. with single 



mediate cones or trefoils ; all grind- developing into double trefoils ; in- 



ers with simple transverse crests ; termediate grinders evolving from 



intermediate grinders evolving from three into four crests, 



two to three crests. I'pper tusks with broad, persistent 



Lower jaw gradually reduced in enamel band on outer concave sur- 



length. face, abrading the lower tusks. 



Inferior canines, rounded tusks, not Lower tusks horizontal, oval or down- 

 functional, turned, with or without enamel 



band. 



