2 86 TABULATE CORALS. 



account the actual transition between an undoubted encrust- 

 ing Ceramopora and an undoubted free and discoidal specimen 

 of Monticulipora petropolitana, Pand. He has examined cer- 

 tain specimens which show characters linking the one on to 

 the other ; but I do not understand him to assert that he has 

 examined specimens which in one portion show the unmistak- 

 able characters of Ceramopora, and which in another, demon- 

 strably older, portion exhibit the features proper to Monticuli- 

 pora. I cannot, however, accept any specimens except such 

 as exhibit as individuals the characters of two types, as being 

 proof that either of the types in question has been developed 

 out of the other. In the second place, apart from this general 

 argument, which may easily be pushed too far, there are very 

 strong grounds for regarding Ceramopora as an independent 

 organism quite distinct from all the forms of Monticulipora. 

 Thus Ceramopora is most abundant in Upper Silurian and 

 Devonian strata, in which Monticulipora are comparatively 

 rare fossils, while the genus is very poorly represented in 

 Lower Silurian strata (such as the Cincinnati formation in 

 North America), in which Monticulipora are excessively abun- 

 dant. An additional proof of the distinctness of Ceramopora 

 is found in the fact that it grows to a large size, preserving 

 unchanged its normal and proper characters, while the general 

 structure and form of its tubes are markedly unlike those of 

 the corallites of the Monticuliporce, being reclined, with oblique 

 and crescentic mouths, and, so far as I have observed, wholly 

 devoid of tabulae. (Dr Lindstrom states that tabulae exist in 

 Ceramopora, but I have been unable to detect these structures 

 in thin sections ; though I have found tabulae in some specimens 

 of a Monticulipora from the Wenlock Limestone of Dudley, 

 which may perhaps be the M. papillata of M'Coy, and which 

 certainly has more of the look of a Polyzoon than is usual in 

 species of Monticulipora^ Moreover, the colonies of Cera- 

 mopora are usually (always ?) fixed, being attached parasiti- 

 cally by a portion or the whole of the lower surface to some 

 foreign body ; whereas the corallum in the discoid species of 



