179 



fibres : the polished dentine shows principally the lines which represent 

 the margins of the hypothetical lamellae which seem to be superimposed 

 and to follow the contour of the grinding surface. The outer surface of 

 the fangs has been water-worn or abraded by some movements of the 

 stratum in which the fossil tooth was deposited. 



From the tertiary deposits of Ohio. Purchased. 



729. The last molar of the left side of the lower jaw of the Mastodon giganteus , 

 The crown supports four transverse ridges and a posterior talon divided 

 into five small transversely disposed mammillae : the crown is supported 

 by an anterior broad compressed fang, two smaller fangs on the same 

 transverse line, and a thick conical fang supporting the posterior half of 

 the tooth ; the end of one of the smaller fangs is broken off, andjke 

 fractured surface exhibits the engine-turned pattern produced by the 

 decussation of opposite curved lines, a character which is so conspicuous 

 in the ivory of the tusks of the proboscidian Pachyderms. The layer of 

 cement which invests the fangs is of great thickness at the angles of their 

 bifurcation. 



From the tertiary deposits of Ohio. Purchased. 



730. The last lower molar of the left side of the Mastodon giganteus : its 



crown supports four transverse ridges and a posterior talon, which from 

 its size and division into two transverse mammilloid processes, resembles 

 a fifth transverse ridge, behind it there is a more minute talon divided 

 into three small tubercles ; a part of the thick coronal cement remains 

 at the bottom of the outer side of the interspace between the third and 

 fourth ridges. A longitudinal vertical section has been removed from 

 the first transverse ridge and its supporting fang, and the enamel has 

 been removed from the remaining part of this ridge, as also from the inner 

 tubercle of the third ridge. A part of the cement has been detached 

 from the dentine of the first, second and posterior fangs, showing the 

 parallel transverse indentations on the surface of the dentine. 



From the tertiary deposits of Ohio. Purchased. 



731. The posterior half of the last molar of the right side of the lower jaw of 

 the Mastodon giganteus : it includes the hinder transverse ridges, a large 



2 a 2 



