GENERA OF CHsETETID^ AND MONTICULIPORID&. 287 



Monticulipora> supposed to be developed out of the former, 

 is usually and normally free ; but it is very difficult to explain 

 this fact if there be any genetic relationship between the 

 two. Thirdly, as regards matters of actual observation, I have 

 never been able to detect anything of the nature of a " Cera- 

 mopora stage" in young Monticuliporce. This is a point 

 which is most easily observed in young examples of the dis- 

 coidal species of Monticulipora, such as M. petropolitana> and 

 the various forms allied to this ; and I can only say that the 

 most minute examples of these forms which have come under 

 my notice differ in no respect whatever, that I can detect, ex- 

 cept size, as regards their external and internal characters, from 

 fully-grown specimens. Fourthly, if it were the case that dis- 

 coidal species of Monticulipora, such as M. petropolitana, Pand., 

 grew out of the thin parasitic crusts to which Hall applied the 

 name of Ceramopora, we ought to be able to detect the primi- 

 tive " Ceramoporoid " portion of the colony at the base of thin 

 vertical sections of colonies of the former. I have, however, 

 examined a large number of such sections, and I have been 

 unable to detect any difference in the structure of the lowest 

 portion of the tubes, resting directly upon the basal epitheca, 

 as compared with that of the fully-grown portion of the coral- 

 lites. Dr Lindstrom states that the basal surface of a Monti- 

 c^ll^pora, when its epitheca is very thin, " clearly shows that it 

 is a Ceramopora" but I am unable to concur in this statement. 

 If the specimen be undoubtedly one of Monticulipora, then I 

 have never seen anything in its epithecal surface which could 

 be compared with the structure of Ceramopora. All that can 

 be said, in my opinion, on this point is that we meet in the 

 Palaeozoic rocks with specimens of the thin discoidal epithecse 

 of certain fossils (the Lichenalia of Hall), which look like the 

 under surface of the epithecal plate of Monticulipora petro- 

 politana, Pand., but which might be really referable to quite 

 different forms, and which mostly cannot, without the prepara- 

 tion of thin sections, be definitely referred either to the Ccelen- 

 terata or the Polyzoa. Lastly, as regards the assertion that 



