vi PREFACE. 



For the benefit of those who may wish to obtain a 

 more detailed knowledge of the subject, or of any special 

 part of it, I have given at the end of the volume a list of 

 some of the more important and easily accessible palaeon- 

 tological works. 



I gratefully acknowledge my indebtedness to Professor 

 McKenny Hughes and Dr G. J. Hinde for advice and 

 help. 



H. WOODS. 



ST JOHN'S COLLEGE, CAMBRIDGE, 

 August, 1893. 



