286 PKOHOSCIDIA. 



The first molar tooth lias a square-shaped crown, broad- 

 est behind, divided into four mastoid tubercles, and aver- 

 ages an inch in length, (antero-posterior diameter,) and 

 three-fourths of an inch in breadth. The second has an 

 oblong crown, supporting three pairs of mastoid tubercles, 

 and averages two inches in length, and one inch one-third 

 in breadth. The third tooth, which takes the place of the 

 above when shed, has a square crown, with two pairs of 

 mastoid tubercles, and an anterior and posterior basal 

 ridge ; it averages a length of two inches, with nearly the 

 same breadth, ranging from one inch and a half, to two 

 inches and a quarter. The fourth tooth has an oblong 

 crown, and supports three pairs of mastoid tubercles, with 

 usually a large posterior tuberculate talon ; its average 

 length is two inches three-fourths; its breadth one inch 

 two-thirds. The fifth tooth resembles the preceding, but 

 averages four inches one-third in length, and two inches 

 three-fourths in breadth. The sixth tooth supports four 

 pairs of mastoid tubercles, and a posterior talon, usually of 

 small size ; its average length is six inches ; its breadth 

 three inches and a quarter. The seventh, and last molar 

 tooth, has generally five pairs of mastoid tubercles, and a 

 posterior tubercular talon ; its average length is seven 

 inches and a quarter, its breadth three inches and a third. 

 The observed extremes of size of this complex tooth, which 

 is subject to more varieties than the preceding teeth, is 

 five inches and a half, and nine inches ; in general the pairs 

 of tubercles gradually and slightly decrease in size from 

 the first to the last : in the small-sized specimens of the 

 seventh molar the decrease is more rapid, and the fifth pair 

 is reduced almost to a tubercular talon, which is succeeded 

 by a small basal ridge ;* in the middle-sized teeth the fifth 



* The tooth in the lower jaw of the Mastodon anffustidens, figured by Cuvier 



