Loomis — An Unusual Mastodon. 



441 



inches in diameter. This individual was an adult which 

 had recently reached maturity as shown by the fact that 

 the last molars are in place and worn, and the epiphyses 

 of the bones are fused to their shafts, except in a few 

 cases those of the vertebrae are still free from the centra. 

 The Nine Mile Bottom individual was older, the last 

 molars being more worn and there being no free 

 epiphyses. This latter individual had longer and larger 

 tusks, the larger one being 14 inches long and 2!/2 inches 



Fig. 2, 



Fig. 2. The lower tusks of the St. Helena Island individual. % nat. size. 



in diameter, and at that the tip is fractured, so that it 

 must in life have been even longer, though not much. 

 These are the largest tusks recorded from the lower jaws. 



Each tusk is completely surrounded by a thick layer of 

 enamel clear to the tip. The ends show hard wear, the 

 enamel being worn through and the tips blunt. On both 

 sets, the outer sides are chipped off and worn smooth, so 

 that this was done during the life of the animals. At the 

 base of each is a wide conical cavity showing that the 

 tusks grew continuously. The large size and extensive 

 wear on the ends indicate that these tusks were of con- 

 siderable functional use to the animals in life, being 

 more worn on the ends than is the case in the upper tusks. 



The St. Helena Island specimen has the last two (fifth 

 and sixth) molars in place in the upper jaw. The fifth 

 is the usual six-point tooth, the points being united by 

 transverse ridges. There are no intermediate cusps and 

 the tooth differs in no way except its large size from the 

 usual American mastodon. It is 43^ inches (118 mm.) 

 long by 3% inches (87 mm.) wide as compared with 101 

 mm. by 77 mm. in the Warren mastodon. The sixth 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 270.— June, 1918. 

 31 



