126 



THE GENUS MONTICULIPORA. 



a variable number of much smaller coralliteS;, which are pro- 

 vided with more numerous and closely-set tabulce. Thirdly, 

 there exists a variable number of very minute, thick-walled 

 tubuli (" spiniform corallites ") which are situated in the thick 

 walls separating the normal corallites, and which are easily 

 recognised by their dark margins. 



Obs. — This pretty little species is readily distinguished by 

 both its external and its internal characters. Externally it is 

 characterised by its smooth surface, without monticules ; by its 







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VoO^ 



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. 20. — Moulicitlipora gracilis, James. A, Part of a tangential section, enlarged eighteen 

 times, showing the two sets of corallites and the hollow spiniform corallites; B, Part of 

 the same section enlarged fifty times ; C, Part of the central axis of the coi^allum, en- 

 larged eighteen times, showing the thin-walled and polygonal condition of the corallites 

 in this region ; D, Part of a vertical section, enlarged eighteen times ; E, A single coral- 

 lite of the same section, enlarged fifty times, showing the fibrous structure of the wall — 

 on one side, the wall is traversed by one of the minute spiniform corallites. From the 

 Cincinnati Group, Cincinnati, Ohio. 



minute, crowded, thick-walled, and oblique calices, with occa- 

 sionally interspersed small tubuli (PL II. figs, la, ib) ; and, to 



