loo THE GENUS MONTICULIFORA. 



small corallites are never so greatly developed as to entirely 

 isolate the large tubes, except in an occasional corallite, nor do 

 they form star-shaped elevated monticules. Even when the 

 small corallites are numerous, their tabulae do not become 

 vesicular, nor are their walls obliterated. Spiniform corallites 

 are commonly present, and may project above the surface as 

 blunt spines ; but they do not form conspicuous surface- 

 columns. 



The above are the principal differential characters by which 

 the species oi Montictdipora proper may be distinguished from 

 those referable to Fistniipora, M'Coy, Constellaria, Dana, or 

 Dekayia, E. and H. As above defined, however, the genus 

 Monticulipora includes a very large number of forms, and the 

 variations in the internal structure of these are so s^reat that 

 it becomes necessary to split up the genus into sections, which 

 must, for convenience' sake, be distinguished by separate names. 

 The work of framing such minor sections is one of the greatest 

 difficulty, and it may reasonably be doubted if our present 

 knowledge has as yet advanced so far that it is possible for 

 us to subdivide this difficult group in more than a merely tenta- 

 tive manner. I have previously (p. 20) given reasons for not 

 accepting the classification proposed by Dybowski, and the 

 arrangement which I propose myself can only be regarded 

 as a provisional one. I formerly (Pal. Tab. Cor., p. 291) pro- 

 posed to divide the group of forms here included under the 

 name of Monticulipora proper into three sub-generic sections 

 — viz., Hcterotrypa, Diplotrypa, and Alonotrypa. After a more 

 extended investigation, however, I propose to add to these 

 three the two additional sections oi Prasopora, Nich. and Eth. 

 jun., and Pei'onopora, Nich., the constitution of the three groups 

 above mentioned being at the same time in some respects 

 altered. I do not pretend that this arrangement is likely to be 

 a final one, but I have endeavoured as far as possible to found 

 my classification upon the aggregate of characters shown by 

 the different species, rather than to base the dividing lines 

 upon single peculiarities of structure, so that I may hope that 



