306 Mr. J. Thomson and Dr. II. A. Nicholson on the 



animation. It seems almost needless to point out that in this 

 way, and in this way only, can any thing like a complete 

 knowledge be obtained of the actual and essential points of 

 structure in the fossil corals. Due weight, of course, should 

 be given to external characters ; but we feel satisfied that the 

 above method of investigation is the only one which is capable 

 of leading to really sound and reliable conclusions, in spite of 

 the great labour and expense which must be attributed as draw- 

 backs to the process. That the general application of this 

 method of investigation to the fossil corals should in some 

 instances yield unexpected results, or possibly even some- 

 what derange existing classifications, is hardly more than might 

 have been anticipated. At the same time, in accordance with 

 a well-known scientific canon, we should not be justified in 

 hoping that even experts will at first accept all the conclusions 

 at which we have arrived, unless they are willing to adopt the 

 same method of investigation *. 



Hitherto the specific determination of the fossil corals of 

 the Palaeozoic formations has very frequently been based upon 

 those points of structure or form which can be made out simply 

 by an examination of the external surface, or of fractured spe- 

 cimens. Only in comparatively few instances have observers 

 had recourse to the more complete research implied by the 

 making of properly prepared sections. That the Palaeozoic 

 corals form a group in many respects peculiarly difficult to 

 study cannot be denied ; but we believe that the difficulties 

 of the case have been much increased by the imperfect modes 

 of investigation which have been in general employed. To 

 this it must be added that few collections of Palaeozoic corals, 

 either public or private, are at present in such a condition as 

 to admit satisfactorily of critical study. 



The generic distinctions amongst the Palaeozoic corals have 

 usually been based upon the characters of the septal system, 

 the presence or absence of a columella and its characters when 

 present, the existence or non-existence of dissepiments and 

 their form and disposition when present, the nature of the 

 tabulae, the characters of the wall and exothecal structures, 

 and the general form and mode of growth of the corallum. 



* Our collections embrace several thousands of cut and polished speci- 

 mens of the Palaeozoic corals, together with a large number of thin sections 

 for microscopic examination, irrespective of very many that have been left 

 in their native condition. No one, who has not learnt by actual experi- 

 ence, can properly appreciate the great expenditure of time, labour, and 

 money involved in thus preparing for examination a large series of fossil 

 corals. Even as it is, much of the material in our hands is still compara- 

 tively unavailable from its not having been submitted to these necessary 

 preliminaries. 



