214 S. CALVIN AFTONIAN MAMMALIAN FAUNA II 



missing on the right side, but the left ramus is complete. The dimensions 

 are: length, 32% inches; height of coronoid, 16% inches; height of 

 articulating condyle, 16% inches. There are sockets for mandibular 

 tusks, and the indications are that these were about equally developed on 

 the right and left sides. The last molars are the only ones remaining, and 

 they are worn to the roots. None of the enamel of the transverse ridges is 

 left, but the thick enamel which covered the outside of the crown forms a 

 continuous ridge around the deeply concave grinding surface. The cup- 

 like feature of the molars is due to rapid wear of the softer dentine in the 

 interior of the tooth, the outside being protected by the rim of harder 

 tissue. 



The deeply concave form of grinding surface, developed by protracted 

 wear, seems to have had serious disadvantages. Both teeth are split ver- 

 tically, as seen in plate 22, and there are indications that the splitting 

 occurred while they were in use, some time before the death of the animal. 

 The sides of the fissures are stained in precisely the same way as the sur- 

 face of the dentine in the bottom of the concavity which characterized 

 the grinding surface, and the angles have been rounded off by evident use 

 since the injury occurred. There is a later, probably post-mortem, frac- 

 ture of the right molar which shows a very different appearance. There 

 is evidence of abrasion and polish on the inner surface of the wall sur- 

 rounding the concave grinding surface, which indicates that the opposing 

 teeth of the upper jaw operated in a way to exert a tremendous wedging 

 or spreading force, and the strain, repeated every time the ponderous 

 jaws were closed, overcame the cohesion of the greatly weakened molars. 

 Only a small amount of the original main body of the teeth remained 

 below the level of the concave grinding surface. 



A last molar of Mastodon mwificus was received from a resident of 

 Missouri Valley, but the specimen had passed through several hands 

 before it came into his possession, and he could give no definite account 

 of where the tooth came from or under what circumstances it had been 

 found. In general appearance and degree of fossilization this specimen 

 agrees with those from the Aftonian. Fossil-bearing Aftonian occurs near 

 Missouri Valley; beyond these statements nothing more definite can be 

 said at present concerning the locality and geological position to which 

 this new molar should be referred. The tooth is much less worn than that 

 illustrated in plate 27, opposite page 355, of the preceding paper. 



OTHER PROBOSCIDEAN REMAINS 



Of the proboscidean remains that can not readily be referred to either 

 the elephant or the mastodon, a few only deserve notice. From the Cox 

 pit there are two well preserved dorsal vertebrae and a large fragment 



