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CHAPTER XXI. 



THE MONTICULIPOROIDS. 



We may consider here the remarkable groups of organisms (Mon- 

 ticuliporidce and Fistuliporidcz), which have been collectively spoken 

 of as the " Monticuliporoids," and the precise systematic position of 

 which is still uncertain. The Monticuliporoids, in fact, exhibit a 

 combination of characters ; and palaeontologists have therefore, so 

 far, come to no final decision as to the true relationships of these 

 puzzling organisms, some authorities regarding them as a peculiar 

 group of Corals, while others consider them to be referable to the 

 Polyzoa. 



The structural characters of the Monticuliporoids are very com- 

 plex, and are for the most part only capable of complete elucidation 

 by means of microscopic examination, while the number of different 

 forms included in the group is very large. For these reasons, noth- 

 ing more will be here attempted than to give a brief outline of the 

 general morphology of the entire series, with the distinctive char- 

 acters of the two families of the Monticuliporidce and Fistuliporidce, 

 and a brief notice of the more important types included in these. 



In all the Monticuliporoids, the skeleton is composed of closely 

 approximated, prismatic or sub-circular tubes, sometimes all similar 

 to one another, sometimes of different sizes, which are provided with 

 distinct walls. In the centre of the colony the tubes are always 

 thin-walled, more or less polygonal in shape, and similar to one 

 another in internal structure ; but as they approach the surface, they 

 diverge from one another by the intercalation of new tubes, their 

 walls commonly becoming at the same time thickened, and their in- 

 ternal characters being modified. It is in the outer, or " mature," re- 

 gion of the colony (fig. 224, e, ni) that a second set of tubes is usually 

 developed in those cases in which the colony is dimorphic. The 

 exterior of the colony commonly exhibits at intervals definite areas 

 ("monticules" and "maculae"), which are elevated or depressed as 

 regards the general surface, and consist of larger or smaller tubes 



