23() 



slightly compressed cylindrical, and curved in their course. They are oval in 

 transverse section, with the long diameter directed from within upward and 

 outward. They are unprovided with enamel, and at the broken ends exhibit 

 the decussating curved lines of structure of the ivory enveloped in a thick 

 layer of dense cementum. At the posterior extremity the broken ends ex- 

 hibit the pulp-cavity occupied with matrix and surrounded with a margin of 

 about a line in thickness, so that the symphysis is broken off near the bottom 

 of the incisive alveoli. 



Frooi the thinning of the anterior alveolar borders of the symphysis it 

 would appear as if the latter was nearly complete, so that if we Siippose the 

 lower tusks projected about 6 inches from the jaw, it would give them an 

 entire length of about 20 inches. 



The breadth of the fore part of the symphysis, in its complete condition, 

 is rather more than 5 inches. At the back part, corresponding with ttie posi- 

 tion of the bottom of the incisive alveoli, it has been about an inch wider. 



The long diameter of the tusks, at their anterior broken ends, is about 20 

 lines; the short diameter 17 lines. These diameters are nearly uniform 

 throughout as existing in the specimen. 



The fore and aft diameter of the last molar tooth, when complete, is esti- 

 mated to have been full (ij inches. The width of the crown at the base of 

 the second and third ridges is 35 lines. The measurements indicate the pro- 

 portioBS of the tooth to be slightly greater than in the corresponding Califor- 

 nia tooth or the cast of the Maryland toyth. 



The depth of the lower jaw below the second ridge of the last molar is 6^ 

 inches ; and the thickness is 5 inches. 



I think it probable, without being positive in the matter, that the Masto- 

 don remains above described, which have been referred to species under the 

 names of Mastodon ob.scurus and M. Shepardi, including those from New Mex- 

 ico, belong to one and the same species. This, from the form of the molar 

 teeth, the constitution of the upper tusks, and the prolonged symphysis of 

 the lower jaw, was clearly a near relation of the Mastodon augustidens of 

 Europe. 



In a note, on page 74, of volume II, of the Palaeontological Memoirs of the 

 late Dr. Falconer, it is stated that at Genoa he had seen a cast of a lower jaw 

 of a mastod'on from Mexico, with an enormous iec abruptly deflected down- 

 ward, and containing one very large incisor. The beak is much thicker than in 



