^ UB- GENUS MONO TR YPA . 



197 



easily recognised by its thin undulated corallum, which carries 

 on both sides the sub-equal, oval, or pentagonal calices, these 

 beino- often arranged in decussatinof lines, and elevated at 

 intervals into low and inconspicuous monticules (PI. VI. figs. 

 3, 3(«). As regards its internal structure, we have seen that the 

 corallites are bilaterally disposed on the two sides of a central 

 plane, as is shown by vertical sections taken at right angles to 



mm ■■ 



(^ / ) o o u ^^ ^ 



MmwK 



41. — Minute structure of M. pavojiia, D'Orb. A, Tangential section, enlarged eighteen 

 times ; B, Part of the same section, enlarged fifty times, showing the structure of the walls 

 of the tubes— in two of the tubes there is a curious tooth-like projection on one side of 

 the visceral chamber ; c, Pai^t of a vertical section, taken at right angles to the flat sur- 

 faces of the corallum, and embracing its entire thickness, enlarged seven times ; D, Part 

 of the preceding section, enlarged eighteen times, showing the central membrane and the 

 remote tabulae. From the Cincinnati Group of Ohio. 



the flat surfaces of the corallum (fig. 41, c and d). All the 

 corallites are of the same kind, approximately equal, and 



