INTRODUCTION. IX 



the sequel), that not only is there no real line of demarcation between 

 Mastodon and Elephas, but several of the species of the two genera 

 seem to pass so imperceptibly into one another, that it is not un- 

 frequently a matter of extreme difficulty (if, indeed, it be not an 

 absolute impossibility) to determine to which species individual 

 teeth really belong. This difficulty is considerably enhanced by the 

 peculiar nature of the dental succession of the Elephantidcv, in which 

 only a moiety of the dental series is ever seen in any one fossil 

 individual ; and we have accordingly to' rely only on their general 

 fades in referring individual teeth to their respective species. In 

 cases, therefore, where two or more closely allied forms occur in the 

 same formation, it will be obvious that such determinations must not 

 unfrequently be more or less provisional and subject to future revi- 

 sion 1 . The Indian Mastodons present especial difficulty in this respect; 

 and I have found it advisable, after much hesitation, to apply specific 

 names to no less than three trilophodont and five tetralophodont 

 forms, some of which have a very restricted distribution. In regard 

 also to the serial position of individual teeth, there must likewise 

 in many cases be a considerable element of doubt, more especially in 

 those instances where a species is liable to great variation in point 

 of size ; thus it is often difficult to say whether a tooth is the last 

 milk-molar of a large individual or the first true molar of a smaller 

 one, or whether a larger tooth should be regarded as a first or a 

 second true molar. In this respect therefore some of the following 

 determinations must also be considered more or less provisional. 

 These two points of uncertainty are, however, not of very great 

 import, and do not in the least interfere with the symmetry of the 

 series from the generalized to the specialized ; and at the most they 

 indicate either that an individual specimen should be referred one 

 degree higher or lower either in the specific series or in the dental 

 series of a particular species. 



Although the object of the present Catalogue is only to record 

 species represented in the Museum Collection, yet in this instance, 

 where we have only to deal with a restricted group containing a 

 comparatively small number of species, it has been thought advis- 

 able to give a list of all the described forms together with their 

 distribution. The following list, which is exclusive of synonymy, 

 comprises all the well-authenticated species of which the writer 

 can find any record ; those species of which he has seen no 



1 For the sake of brevity a provisional determination is only mentioned in 

 the text in some of the most doubtful cases. 



