50 THE GENUS MONTICULIPORA. 



eral, truly dimorphic, quite as genuinely as in Heliopora or 

 Heliolites. One set of corallites may be much reduced in 

 number, or may undergo much modification, but I believe that 

 the existence of two different kinds of tubes can usually be 

 demonstrated ; and the importance of this fact, from a theo- 

 retical point of view, can hardly be overestimated. At the 

 same time, there are forms, otherwise quite resembling the 

 dimorphic species, in which all the corallites of the colony 

 are apparently similar in their internal structure, and approx- 

 imately equal in size ; so that we are not able to assert posi- 

 tively that the corallum in Monticulipora invariably consisted 

 of two different sets of tubes. 



The nature and relative development of the two sets of cor- 

 allites which are usually present in Monticulipora constitute 

 important elements in the framing of any classification of the 

 numerous forms included under this general name ; though 

 other considerations must be taken into account as well, if such 

 a classification is to be in any way natural. Leaving this 

 aspect of the question aside in the meanwhile, the following 

 are the principal variations exhibited by different forms of 

 Monticulipora as regards the nature and arrangement of the 

 corallites : — 



A. Forms with a single series of corallites, which exhibit no marked differences 



in internal structure. 



a. Without spiniform corallites, and without well-marked groups of 



large or small tubes. Ex., M. quadraia, Rom., M. Winteri, Nich., 

 Af. irregularis, Ulrich, M. clavacoidca, James. 



b. Without spiniform corallites, but with well-marked groups of large 



tubes. Ex., M. pulchella, E. and H., M. nndulata, Nich., M. 

 petasiformis, Nich. 



c. With spiniform corallites, but without well-marked clusters of large 



or small corallites. Ex., AT. discoidca, James, M. moniliformis, 

 Nich., Af. Barrandii, Nich. 



B. Forms with two sets of corallites, large and small, the small tubes being much 



more closely tabulate, or otherwise differing in structure from the large 



ones. 



a. With no spiniform corallites, with or without clusters of large tubes. 

 Ex., M. petropolitana, Pand., A£. Newberryi, Nich., AI. Cincin- 

 7iatiensis, James, M. Andrezvsii, Nich., M. {Prasopord) Grayce, 

 Nich. and Eth. jun., AI. molcsta, Nich. 



