84 THE GENUS MONTICULIPORA. 



internal structure above (fig. 12). It was also noticed by 

 Mr Lonsdale, in his descriptions of the species upon which 

 he originally founded the genus (Darwin's ' Geological 

 Observations on the Volcanic Islands,' Appendix, 1844). 

 Somewhat similar phenomena are, however, observable in 

 some AIontiadipoi'cE I and the character in question, so far 

 as I have observed, is never more than a partial one in 

 any species of Stenopora. That is to say, most of the 

 calices in Stenopora will be found to be open, and it is only 

 in some of them — generally in patches — that these peculiar 

 perforated diaphragms can be detected. As a test of the 

 relations of any given specimen, this character, therefore, can- 

 not be relied upon. Another and a very striking feature, arising 

 out of the preceding peculiarity, may be occasionally observed 

 in longitudinal sections of the corallites of Stenopora ; and that 

 is, that certain of the tabular are perforated by a central aper- 

 ture, thus showing themselves in section as two opposing 

 ledges running out from opposite walls of the corallites, but not 

 meeting in the centre. This remarkable imperfection of the 

 tabulae is one of the most striking characters of Stenopora 

 Howsii, Nich. ; but even this form possesses some tabulae which 

 seem to want this perforation (fig. 12, b), and I have not 

 observed the same thing in any other species of Stenopora. 

 Upon the whole, therefore, the most readily determinable 

 peculiarity, and the one which appears to be most universally 

 present, is the periodic thickening of the walls of the coral- 

 lites in their outer portions in Stenopora, as compared with the 

 uniform thickening, or the absence of thickening, which is 

 characteristic of the corallites of Monti cttiipoj'a. 



The more massive species of Alonticiilipora, such as ]\I. 



portion of their course. Tabula; sometimes complete, sometimes with a central 

 perforation. No septa. Mural pores not observed. 



The only specimens of this remarkable species that I have seen were collected by 

 Mr Howse in the Carboniferous shales of Redesdale, Northumberland, and it is to 

 his kindness that I am indebted for the opportunity of examining them. I shall 

 describe them at greater length on another occasion ; but in the meanwhile the 

 above brief diagnosis will serve to characterise the species. 



