156 Mr. J. Young on Ure’s “Millepore.” 
The external characters of Ure’s “ Millepore”’ vary some- 
what in its several stages and in different specimens. In 
young examples the cells are bounded by thin walls, and the 
openings are polygonal. In older specimens the outer walls 
become much thickened, and the cell-openings are round or 
oval. In well-preserved specimens the outer surface of the 
walls is often seen to be minutely tuberculated or spinose, 
these tubercles, in polished sections, appearing as small 
pores in the walls; but they are not tabulated. Other, larger 
pores that exist in the walls at the angles between the larger 
cells, became filled with perforated tabule, like those in the 
tubes of the larger corallites, as the organism increased in 
diameter ; but both of these sets of smaller pores disappear in 
the walls as sections of branches are ground from thei sur- 
face to near the central axis, the walls there becoming thin 
and the cells polygonal, as seen in the earlier stage of the 
organism, 
Ure’s “ Millepore”’ has macule on its external surface, 
and on one incrusting specimen that I have examined, these 
macule rise into distinct monticules. They are best seen on 
incrusting specimens of the organism, but are also to be found 
on many of the branching examples. 
The macule are generally about 2 lines apart, and consist 
of spots in which are grouped a few very small cells, around 
which there are other cells that are somewhat larger in their 
openings than those of the normal size that fill im the spaces 
around the various macule. 
The perforated tabula, which form the distinctive internal 
character of Ure’s “‘ Millepore,” can be seen in nearly every 
specimen in which the structure has not been too much de- 
stroyed through mineralization of the organism. In the lime- 
stone shales of the East Kilbride district, where Ure obtained 
his specimens, it is abundant in several localities, but gene- 
rally in fragments of branches. H any of these are rubbed 
down on a fine polishing-stone a little distance below the 
surface and at right angles to the mouths of the corallites, 
the perforated tabule are readily seen. Having prepared 
numerous specimens, both as transparent and opaque sections, 
for examination under the microscope, I find that those which 
show the tabule in the greatest numbers within the corallites 
are the opaque sections. ‘l'his arises from the fact that the 
branches are often curved, and that the tabule do not all lie 
in the tubes at the same level, so that in flat sections only 
those few tabula that happen to be at the surface remain after 
grinding the specimens to transparency; while in opaque 
sections we not only see those perforated tabule that are at 
