236 



AMEEICAN FOSSIL ELEPHANTS. 



elements of undoubted authenticity, presented together in 

 the same individuals. But entire skulls are very rare, and 

 it is only under favourable circumstances that entire man- 

 dibles are met with ; while the dense, hard, and more 

 durable molars occur everywhere. Practically, therefore, the 

 identification of the species, in most instances, rests upon 

 them : and the characters which they yield are so constant 

 and well marked, that, with care on the part of the observer, 

 they are perfectly reliable and sufficient for the purpose. In 

 the London collections, taking those of the British Museum 

 and College of Surgeons together, abundant materials exist 

 for the comparison of molars of the American Mammoth with 

 those of the Siberian and European forms. The Hunterian 

 collection contains a fine series of palates with teeth, lower 

 jaws, and detached molars of the Mammoth, from different 

 localities in the United States. The vast collection in the 

 British Museum includes numerous remains of the species 

 from Eschscholtz Bay and Siberia, accessible for ready com- 

 parison with British specimens. They all present, in the 

 main, the same characters : a uniform ridge-formula ; the 

 same obtuse form of the lower jaw, and the same broad- 

 crowned molars, composed of closely compressed colliculi, 

 with numerous digitations and attenuated uncrimped enamel- 

 plates. The space within which the present communication 

 is necessarily limited prohibits my entering into the details 

 of the comparison. One of the most essential points is to 

 determine the constancy of the ridge-formula, which, after the 

 examination of a very large quantity of materials, I believe in 

 the Mammoth to be thus : 



Milk molars. 



True molars. 



4, 8, 12 _ 12, 16, 24 

 4, 8, 12 : 12] 16, 24 



the consecutive ciphers indicating above and below, the num- 

 ber of colliculi which normally enter into the composition of 

 the antepenultimate, penultimate, and last milk molars in the 

 first groups, and in the second, those of the three true molars. 

 The plates advance by quaternary increments in each series, 

 bearing in mind that the first true molar, although of larger 

 dimensions, commonly repeats the number of ridges presented 

 by the last milk molar, and that the last true molar in all the 

 Elephants and Mastodons is more composite than the others. 1 



1 I take this opportunity of indicat- 

 ing a correction in the 'ridge-formula' 

 of the subgeneric group Euelepkas, given 

 in my memoir ' On the Species of Mas- 

 todon and Elephant,' contained in vol. 

 xiii. of the Quarterly Journal of the 



Geol. Society, 1857, p. 315. Instead of 

 the ciphers 



Milk molars. True molars. 



4, 8, 12,: 14, 18, 24, 

 4, 8, 12, 14, 18, 24-27, 



