PREFACE. Vll 



space. Finally, the minute structure of the skeleton in different 

 groups of animals, and particularly in the lower types, has been 

 treated of as fully as the limits of the work have allowed. 



Owing to the circumstance that a large portion of the first volume 

 of this work has been in type for a considerable time, the Authors 

 regret that they have not been able to avail themselves fully, or at 

 all, of some recent publications, of both a general and a special 

 nature, such, for example, as Neumayr's ' Die Stamme des Thier- 

 reichs,' and the newly published volume of Barrande's monumental 

 work dealing with the Cystideans. In an Appendix to the second 

 volume attention is, however, directed to certain points of importance 

 which have emerged during the passage of this work through the 

 press. Such errors as have been recognised will be found in a list 

 of Corrigenda at the end of the Table of Contents to each volume. 



To many of their fellow-workers the Authors have to express their 

 obligation for direct or indirect assistance in their task. To no 

 one is this more largely due than to Professor Karl von Zittel, to 

 whose masterly ' Handbuch der Palseontologie ' they have been on 

 many occasions indebted for guidance in questions of doubt or diffi- 

 culty. The very special gratitude of the Authors is due to Dr P. 

 Herbert Carpenter for the most valuable assistance in the prepara- 

 tion of the chapters dealing with the Echinoderms, as also to Mr 

 A. Smith Woodward and Dr R. H. Traquair for much information 

 concerning fossil Fishes. They have likewise to express their best 

 thanks to Dr George J. Hinde, Dr H. B. Brady, Dr Henry Wood- 

 ward, Professor T. Rupert Jones, Mr A. H. Foord, Mr John Young, 

 and others of their fellow-workers, from whom they have received 

 much friendly help. Finally, the Authors have to express their 

 gratitude to those who have assisted them by allowing them the use 

 of illustrations. Amongst those to whom thanks are due on. this 

 score are M. Louis Dollo, Professors H. F. Osborne and W. B. 

 Scott, Professor A. Gaudry, Professor E. D. Cope, Professor O. C. 

 Marsh, Professor E. Koken, Dr Anton Fritsch, Dr Henry Wood- 

 ward, the Director of British Museum (Natural History), the 

 present and late Directors of the Geological Survey of India, and 

 the Director of the Geological Survey of Canada. 



