VI PREFACE. 



doubled in number. The present edition may therefore be con- 

 sidered as, to all intents and purposes, an entirely new work. The 

 Authors also trust that this edition will be found to have gained 

 much from the fact that the Invertebrates and Vertebrates have 

 been dealt with by different writers. 



With regard to the general plan of the work, the Authors need 

 only say that the Invertebrate and Vertebrate animals have been 

 treated of as fully as considerations of space would permit ; while 

 the fossil plants have been dealt with in a comparatively summary 

 fashion. This course has been followed primarily on the ground 

 that Palaeozoology is of much greater importance to the general 

 student than is Paleobotany ; but it has been also dictated by the 

 consideration that the latter subject is one of great complexity, and 

 is at the same time one upon which neither of the Authors has any 

 claim to speak with authority. It did not seem advisable, however, 

 to entirely omit the subject of Paleobotany ; and an attempt has 

 accordingly been made to give such a general summary of the pres- 

 ent condition of our knowledge of this department as may be found 

 useful to those studying Palaeontology as a whole. 



In dealing with the vast mass of facts constituting the modern 

 science of Palaeontology, much has been, necessarily, omitted ; while 

 the Authors can scarcely hope that errors have been altogether 

 avoided. Moreover, in its present condition of rapid growth and 

 development, Palaeontology presents many questions — sometimes 

 affecting points of fundamental importance — upon which the opinions 

 of different investigators are widely divergent. It is, therefore, in- 

 evitable that there should be many questions dealt with in the pres- 

 ent work in regard to which the opinions expressed by the Authors 

 differ from those held by other workers in the same field. The 

 Authors can only hope that on such controverted points they have 

 not expressed themselves too dogmatically ; and that, while the 

 limits and scope of the work would not admit of any detailed dis- 

 cussion of divergent views, the existence of such has nevertheless 

 been generally indicated. It may be added that where a definite 

 position has been taken up upon a controverted question, this has 

 been, in general, the result of original investigation on the part of 

 the writer. Theoretical questions, again, have been for the most 

 part avoided, partly because of their unsuitability for discussion 

 in a work intended for students, and partly also from want of 



