158 THE GENUS MONTICULIPORA. 



Corals' (1879), I was unfortunately ignorant of even the 

 existence of Dybowski's treatise ; and the description of the 

 characters of the present species which I published at that 

 time, and which is here reproduced, was based upon specimens 

 from the Lower Silurian deposits of Sweden, for which I was 

 indebted to the kindness of my friend Dr Lindstrom. 



Starting, therefore, upon the basis that microscopic examina- 

 tion by means of thin sections is essential to any safe progress 

 in identifying the various types of the Alontmiliporcs, it is 

 clear that all determinations of the present species w^iich are 

 founded simply upon resemblances in external form and sur- 

 face-characters are absolutely useless and unreliable. Thus, 

 all the corals which I have myself examined and described 

 from the Lower Silurian rocks of North America, and which 

 I have formerly identified with M. petropolitana, Pand., on 

 account of their general form and appearance, turn out on 

 microscopic examination to differ widely in internal structure 

 from the similar-looking Russian species. In fact, I am now 

 acquainted with some half-dozen types, which all more or less 

 closely resemble the true M. petropolitana in external char- 

 acters and form, but all of which, as tested by the facts of their 

 minute structure, are distinct from this, and distinct from one 

 another. Considering, therefore, that almost all the determina- 

 tions of M. petropolitana, in different deposits and in different 

 countries, have been based solely upon macroscopic investiga- 

 tion, and that this is clearly insufficient for specific diagnosis, 

 it has appeared to me to be quite useless to give any synonymy 

 of the species. With our present knowledge, in fact, such a 

 synonymy would simply give us the information that certain 

 authors had identified from certain regions and formations 

 corals which are doubtless referable to Monticulipora in its 

 wide sense, and which resemble ]\L petropolitana in form and 

 habit. 



In the Swedish specimens of M. petropolitana, Pand., which 

 I shall take as the type of the species, the corallum has the 

 well-known hemispherical or sub-globular form, its circular and 



