Tetrabelodon lulli. 91 



angustidens. The condyloid process is constricted into a dis- 

 tinct neck below the condyle. The condyle is large, elliptical 

 in outline and noticeably convex. This is very unlike Eube- 

 lodon morrilli* in which the convexity is extremely low. 

 The condyle measures ±\ inches (114 mm ) transversely, by 2f 

 inches (69 ram ) postero-anteriorly. The condylar surface lies 

 7i inches (191 mm ) above the crown of the molars. The extreme 

 distance across the condyles is 23^- inches (597 mm ). 



The coronoid process resembles that of a typical mammal, 

 but differs widely from any living or fossil elephant with 

 which we are familiar. It is deeply roughened for ligamentous 

 attachment, and is strongly recurved. The lower of the three 

 mental foramina is produced into a deep, narrow fossa 10 

 inches (254 mm ) long. The foramen itself is noticeably large, 

 and must have admitted great nerves and vessels. The same 

 condition obtains in the new mastodon, Eubelodon morrilli, 

 from Brown County. In Tetrabelodon willistoni^ from the 

 same beds, the foramen is large and elliptical, but only moder- 

 ately produced. In Mastodon americanus, the mental fora- 

 men ordinarily lies below the front edge of molar No. 2. In 

 the mammoths and modern elephants, these foramina are small, 

 in many cases numerous, and close to the symphysial line. 



The mandible of Tetrabelodon lulli is from an individual 

 advanced in age. The teeth are worn flat and low and are 

 deeply cupped at each of the four transverse ridges. Two 

 cones, indicated by concentric rings, are discernible in each 

 ridge, but no secondary cones are apparent. Contrary to the 

 usual order, the teeth are ground with an inward and back- 

 ward slant. The back slant on the last transverse ridge is 

 noticeably steep. The molars are 8f inches (222 mm ) long, by 

 3|- inches (89 mm ) wide. 



After an immeasurably extended period of survival, wide 

 migrations, and various modifications, the longirostral masto- 

 dons gradually merged into the brevirostral. Many stages of 

 development are already known, and many more are to be dis- 

 covered. The Nebraska beds seem destined to furnish many 

 links in the phylogeny of the Proboscidea. It seems certain 

 also that many subdivisions must be made in the group. Even 

 after the mastodons became short-jawed, they continued to 

 bear one or two dwarfed mandibular tusks. This obtains in 

 the case of Mastodon americanus, which survived almost to 

 modern times, and in which one or two small lower tusks are 

 occasionally found. 



The maxillary tusk found associated with this mandible is 



* Barbour, ErwinH.: Mammalian Fossils from Devil's Gulch, Nebr. Geol. 

 Survey, vol. iv, pt. 11, No. 33. 

 f Idem. 



