INTR OD UCTION. xxiii 



In attempting- the execution of this plan, considerable 

 difficulties have been met with in all departments, and 

 the writers would claim indulgence for the numerous 

 imperfections which critical studies must soon reveal. The 

 publication of undefined names, for instance, has been a 

 source of much inconvenience, especially among the 

 Reptilia, in which a single University Museum is respon- 

 sible for no less than seventy meaningless terms ; and the 

 numerous hasty publications upon the same subject, which 

 have appeared within recent years, have tended in no 

 small degree to add to the confusion. 



While wholly responsible, however, for whatever im- 

 perfections the work may contain, the writers are deeply 

 indebted to the kindness of numerous friends and specialists 

 in various departments, who have freely given advice, and, 

 in many cases, read the proofs. To Mr. William Davies 

 thanks are especially due for continual help, he having read 

 the whole of the proofs, and given the writers the benefit 

 of his long experience in connexion with the Fossil Verte- 

 brata in the British Museum. To Dr. R. H. Traquair, 

 F.R.S., Mr. James W. Davis, and Mr. John Ward, the 

 writers are especially indebted for information concerning 

 Palaeozoic Fishes ; and the accepted synonymy of the 

 Coal-Measure Amphibia of Northumberland has been 

 contributed by Mr. William Dinning, of Newcastle, The 

 proofs of the Dinosaurian Reptiles have been read by Mr. 

 J. W. Hulke, F.R.S.; and Mr. R. Lydekker has favoured 

 the writers with continual advice concerning the higher 

 Vertebrata, besides kindly permitting reference to numerous 

 unpublished proof sheets. The section on Aves has been 

 read by Mr. R. Bowdler Sharpe and Mr. E. T. Newton, to 

 the former of whom is due the accepted nomenclature of 

 the recent species. To Mr. G. A. Boulenger the writers 

 are indebted for the revision of the nomenclature of recent 

 Amphibia and Reptilia, in addition to numerous other 

 notes ; and Mr. Oldfield Thomas has kindly advised on all 



