PREFACE TO THE SECOND EDITION. 



THE present edition of this work has not only been entirely 

 revised and largely re-written, but it has been so largely 

 augmented by the addition of new matter, that it may be 

 considered as to all intents and purposes a new book. In 

 the former edition, the final section of the work was devoted 

 to Historical or Stratigraphical Palaeontology ; but this sub- 

 ject has been entirely omitted on the present occasion, as 

 it is most suitably dealt with separately, and it has been 

 treated of in a general manner in the Author's 'Ancient 

 Life-History of the Earth.' 



As in the former edition, considerably more space has 

 been allotted to the Invertebrata than to the Vertebrata, for 

 reasons which are obvious, and especially upon the ground 

 that palseontological students are, as a rule, much more largely 

 concerned with the former than the latter. An attempt has 

 also been made to give, as far as possible, brief and general 

 definitions of the more important and widely distributed 

 families, or even genera, of the Invertebrata, as well as, to 

 a more limited extent, of the Vertebrata. In carrying out 

 this attempt, however, it is clear that it was necessary to 

 make a rigid selection of material, based upon what might 

 appear to be the relative importance of different types. All 

 conclusions upon this subject must, however, be matters of 



