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INTRODUCTION. Xxill 
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 
Paleozoic 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unpublished proof sheets.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 
