2i8 THE GENUS MONTICULIPORA. 



by small tubes, either alone or with a few tubes of larger size 

 mixed with them. Different specimens, however, vary con- 



Fig. 46. — The minute structure of Moiiticulipora frondosa, D'Orb. A, Part of a langenlial 

 section, enlarged eighteen times ; B, Part of the same section, enlarged fifty times, show- 

 ing the large tubes with their singular incomplete tabula;, the smaller intercalated tubes, 

 and tlie numerous spiniform corallites ; C, Part of another tangential section, taken at a 

 deeper level than the preceding ; D, Part of a vertical section, at right angles to the flat 

 i-urfaces of the corallum, showing the peculiar form of the tabulte in the large corallites, 

 enlarged eighteen times. From the Cincinnati Group of Ohio. 



siderably as to the extent to which these clusters of small tubes 

 are elevated above the general surface. Sometimes, especially 

 in young examples, they may not be perceptibly elevated at 

 all ; but more commonly (PI. V. fig. 5), they are so far raised 

 as to constitute low rounded "monticules." In no case, how- 

 ever, are the monticules so conspicuous as they are in M. mo- 

 Icsta, Nich., M. Dawsoni, Nich., and most examples of M. 

 nianimiilata, D'Orb. 



As regards its internal structure, ]\I. frondosa^ D'Orb., ex- 

 hibits features of a very remarkable character. In tangential 

 sections which are taken just below the surface (fig. 46, a and 



