144 THE GENUS MONTICULIPORA. 



The spaces between the ordinary caHces may appear almost or 

 quite solid, but in other specimens the apertures of a larger or 

 smaller number of small variably-shaped interstitial tubes may 

 be recognised ; while blunt tubercles or spines, representing 

 the upper terminations of " spiniform corallites," can sometimes 

 be detected on the margins of the calices. Surface smooth, or 

 with barely perceptible eminences, sometimes with a few irreg- 

 ularly disposed stellate maculae, which are not raised above 

 the Q-eneral surface, and seem to consist of small tubules. 

 Large corallites angular, polygonal, and thin -walled in the 

 centre of the branches ; but becoming thickened as they ap- 

 proach the surface, each being in the outer portion of the 

 branches surrounded by a distinct ring-like wall. Small in- 

 terstitial corallites very variable in size and shape, occupying, 

 all the intervals between the large corallites. Between the 

 latter, also, or in the substance of their walls, are developed 

 numerous thick-walled, circular or oval, darkly-outlined tubuli 

 ("spiniform corallites"). Tabulze wanting, or very sparsely 

 developed in the axis of the branches; remote in the larger 

 corallites, but numerous and close -set in the small tubes. 

 In all cases the tabulae are complete, and are horizontal or 

 slightly bent. 



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Firr. 25.— A, Fragment of the corallum of MonticuUpora Jamcsi, Nich., from the Cincinnati 

 Group of Ohio, of the natural size. B, Part of the surface of the same, enlarged. This 

 figure is apt to convey the erroneous impression that the apertures of the large corallites 

 'are raised above the general surface ; but this is not really the case. 



Obs. — The superficial characters of this well-marked type 

 (fig. 25) arc sufficiently treated of in the preceding diagnosis ; 



