SUB- GENUS HETEROTRYPA. 



145 



but I may give a short account of the appearances presented 

 by thin sections. In tangential sections (fig. 26, a and b) the 

 greater part of the section is seen to be occupied with the 



Fig. 26. — Thin sections of Montiailipora Janiesi, Nich. A, Part of a tangential section, 

 taken just below the surface, enlarged eighteen times, showing the large and small coral- 

 lites and the interspersed spiniform corallites. B, Part of the same section, enlarged fifty 

 times. C, Part of a transverse section of a branch, in the axial region, enlarged eigh- 

 teen times, showing the thin-walled, polygonal, and unequal-sized corallites of this part 

 of the corallum. D, Part of a longitudinal section in the median plane, showing the 

 corallites in the outer portion of their course, where their walls are thickened : the sec- 

 tion shows the larger and smaller corallites, the former with remote, and the latter with 

 close-set, tabulse. From the Cincinnati Group, Ohio. 



rounded or oval apertures of the large corallites. The walls 

 of the corallites are largely thickened by a secondary deposit 

 of sclerenchyma, but in all cases the thin dark lines mark- 

 ing the original boundaries between contiguous tubes can be 

 readily recognised, the precise appearances exhibited varying 

 with the depth below the surface at which the section may 

 be taken. Thus, in some sections the large and small tubes 

 alike can be seen to be bounded by distinct delicate dark lines, 

 which represent the original walls, and which show that all the 



K 



