THE GENUS MONTICULIPORA. 



rounded. On the other hand, in tangential sections taken 

 at a somewhat deeper level (fig. i8, a and b) the marginal 



Fig. 1 8. — Internal structure of Montiailipora raniosa, E. and H., from the Cincinnati Group 

 of Ohio. A, Tangential section, taken at a little distance below the surface, showing the 

 two sets of corallites, enlarged eighteen times ; B, Portion of the same section, enlarged 

 fifty times ; c, Part of another tangential section, taken just below the surface, enlarged 

 fifty times; D, Part of the exterior of a vertical section, enlarged eighteen times, show- 

 ing the different tabulation of the large and small corallites; E, Part of the same section, 

 enlarged fifty times, showing the structure of the wall in the outer zone of the branches. 



rings of the larger corallites are more completely separated 

 from one another, and the small corallites are increased in 

 size by the reduction of their bounding-walls, while their 

 shape becomes more or less angular. 



Vertical sections (fig. i8, d and e) show that the internal 

 structure of the large and small tubes is conspicuously different, 

 both sets of corallites being traversed by complete horizontal 

 tabulae, which are greatly more numerous in the small tubes 



