PREFACE. 



THE brief sketch of our present knowledge of extinct 

 vertebrated animals attempted in this volume, is in- 

 tended for students of Vertebrate Morphology and Zoology who 

 are desirous of examining in detail the palaeontological aspect 

 of their subject. The advanced student has long appreciated 

 the necessity for a more extended acquaintance with the facts 

 of Embryology on completing his elementary course : he now 

 begins to perceive that to understand the varied problems 

 aright, he must also enter somewhat minutely into the past 

 history of life on the globe as revealed by Palaeontology. The 

 latter task in most cases proves more difficult than the former, 

 since the trained powers of observation needed for interpreting 

 the remains of organisms embedded in rock are somewhat 

 different from those acquired in the study of fresh tissues and 

 organs. Moreover, much of the essential literature of the 

 subject is contained in unfamiliar works and serials dealing 

 chiefly with rocks and minerals. An elementary handbook, 

 presenting only the broad outlines of this branch of biological 

 enquiry, will thus perhaps be found useful as an introduction 

 to more elaborate treatises and original memoirs, which are 

 difficult to understand without some preliminary idea of 

 general principles. 



It is hoped that the plan adopted in the following pages 

 will facilitate the comprehension of these general principles. 

 The more important facts and generalizations are., printed in 

 large type ; while the more technical and descriptive matter, 

 which ought to be studied with specimens in a museum, is 

 intercalated in paragraphs of small type. Each of these 

 technical paragraphs deals with a typical genus which is 

 comparatively well-known ; and the description is not a generic 

 diagnosis, but merely a statement of the principal facts already 

 ascertained concerning the fossils on which our knowledge of 



