318 Mr. J. Thomson on a 



creation of a new genus for its reception was suggested. 

 This, however, seems to be unnecessary. Subsequent in- 

 vestigations have revealed that reproduction in this and 

 the accompanying genus LitJiostrotion, Luidius, may be 

 either by calicular gemmation or by fissiparity. Indeed, I 

 hope by-and-by to demonstrate that we cannot restrict generic 

 identity, not only in this but also in several other genera, by 

 the mode of development. While the union of the corallites 

 and consequent prismatic aspect is new to the genus, yet we 

 cannot overlook the fact that our knowledge of the Carbon- 

 iferous fauna is fragmentary and imperfect ; but when moi'e 

 complete other forms will no doubt be discovered showing 

 even a closer relation to its nearest ally Lithostrotion. 

 A similar objection to the union of the cylindrical and pris- 

 matic varieties in the genus Lithostrotion was long accepted ; 

 but the generalization of those great masters Mihie-Edwards 

 and Jules Haime showed that external aspects so dissimilar 

 were not incompatible with generic identity, and that we can 

 define genera oidy from the internal structural characters — a 

 decision which, from the enormous amount of evidence in my 

 hands, I cordially endorse. All the other structural details 

 being similar to those characteristic of the other species of the 

 genus, we are justified in believing that the creation of a 

 new genus on the union of the corallites would be adding an 

 unwarranted synonym to the list of Carboniferous corals. 



Diphyphyllum Argyllii^ sp. no v. 



Fi-. 1. 



