PREFACE. 



Nearly six years have elapsed since the publication of the third volume of this 

 Catalogue. The causes of the delay in the appearance of this fourth volume are 

 explained by the author in his Introduction. 



This volume deals with Goniopora, which was always thought to be a small 

 o-enus of purely recent reef corals. Mr. Bernard's study of the rich collection of 

 fossils contained in the Geological Department, a study undertaken at my request, 

 has revealed the fact that an important Tertiary coral (Litharcea) is generically 

 identical with Goniopora ; the genus can now he traced back to early Cretaceous 

 times, and seems to have had a period of maximum development in the early 

 Tertiary beds of South Europe. The fossils, moreover, threw much new light, 

 which could not otherwise have been obtained, upon the morphology of the genus. 

 The variability of the corals has, in previous volumes, been a good deal 

 obscured by the establishment of a number of so-called species ; the author has 

 thought it right to cease establishing genetic groups without the necessary data 

 for so doing. He regards his task as that of presenting the facts and what may 

 legitimately be deduced from them in the way that will be most useful to future 

 workers, and to the officials of other Museums. Experience alone can show 

 whether the method he has adopted in order to attain this end, however fault- 

 less its logic may be, can be employed with advantage in dealing with any 

 other group besides the corals, or even whether it is the best way of presenting 

 the corals, having regard solely to the facts. The attempt is, however, a sign of 

 the times, for it is clear that, whether the older school of systematists like it of 

 not, the question of method is an increasingly serious one, and Mr. Bernard's 

 attempt should stimulate inquiry outside the beaten paths. 



