COLUMNARTAD^. 189 



The apparent absence of mural pores renders it impossible to 

 refer Lyopoj^a to the FavositidcB ; and the undoubted absence 

 of " coenenchymal tubules " entirely precludes any comparison 

 between it and the Helioporidcs. Under these circumstances 

 it is very difficult to state anything definite as to the systematic 

 place which the genus ought to occupy. Its general characters 

 are in many respects such as to approximate it to Cohwmaria, 

 Goldfuss, which will be discussed immediately ; but this can 

 hardly be said to make matters any clearer, for the precise 

 zoological relationships of the latter are still very uncertain. 

 Moreover, a close comparison of specimens and thin sections of 

 these two genera has convinced me that the points of resem- 

 blance between them are largely counterbalanced by points of 

 structural dissimilarity. Thus the typical forms of Cohcmnaria 

 not only want the extraordinarily thickened walls of Lyopoi^a, 

 but possess a septal system, which, even in its most rudimentary 

 condition, is a marked advance upon that of the latter ; while 

 the amalgamation of the walls of the corallites is never carried 

 to the extent of in any way obliterating or obscuring the line of 

 demarcation between contiguous tubes. The typical species of 

 Columnaria, indeed, present many features which would induce 

 us to place them among the Rugose Corals, whereas Lyopora 

 exhibits no characters save such as were supposed to be dis- 

 tinctive of the old group of the " Tabulata." Upon the whole, 

 therefore, I must at present leave the position and zoological 

 relationships of Lyopora entirely open questions. 



So far as known, the geological range of the genus Lyo- 

 poi'a is an extremely limited one, the only recorded species 

 being the L. favosa, M'Coy, sp., of the Lower Silurian rocks of 

 Ayrshire. I subjoin a brief diagnosis of this singular species, 

 extracted from the * Monograph on the Silurian Fossils of 

 Girvan,' by Mr R. Etheridge, jun., and myself. 



