8 
variation in internal structure. In reasonably well-preserved specimens 
the septa can be seen at the surface as very short and wedge shaped. The 
surface of a longitudinal break down the corallum shows, when weathered, 
the very typical cribriform appearance of the interior of the corallite. 
Here the septa can be seen as low, vertical ridges produced about every 
0*5 mm. into short, wedge-shaped spines, which are contiguous at their 
bases with their neighbours on a horizontal plane, and thus lie in vertical 
and horizontal rows. Alternating with these septal spines, and owing their 
presence to a lack of fusion between the septa except at these regular and 
limited regions, are well-developed mural pores. These may appear as 
quadrangular, oval, or circular, depending on preservation and the depth 
of weathering. 
The internal structure of this species is very distinct. In transverse 
sections many of the corallites appear as circular (but only in that the 
polygonal shape is roughly rounded off), and the "wall” separating them 
may present one of two aspects, depending on the immediate horizon of 
the section. If it is cut where the septa are in contact, this “ wall ” is 
solid, with short, wedge-shaped spines arising from it alternately on one 
side and the other; but where it is cut through an horizon where the septa 
are not in contact, which is usually for a greater distance than that for 
which they are, the " wall ” is seen to be represented only by sections of 
isolated septa, separated from their neighbours by a varying width of pore. 
In such sections the original alternate arrangement of the septa in adjoining 
corallites may be lost, one unit extending straight from one corallite to 
the next. 
It can be seen, then, that there is no true wall, and the corallites are 
bounded by an open lattice work of septal elements, recognizable in either 
longitudinal or transverse sections by the radiation of fibres that con- 
stitute them. From the point of view of description, Nicholson’s trivial 
name for this species, cribriformis^ although invalid, is a particularly 
happy one. The situation in Favosites, with which Billings compared the 
pores of this genus, is very different; for there a definite wall is developed 
and pores pierce it, and sometimes, even, there is a collar-like thickening 
of the wall around them. 
In longitudinal section the periodic raising of the septal ridges to 
spines, already described from the external appearance, is well seen, giving 
the corallite boundary, if no pores are cut, a serrate appearance inward, 
with the spines, which dilate constantly toward their bases, directed 
slightly upward. The "dark line” of Ogilvie (1896) is in many cases 
visible in transverse sections of septal ridges or spines where, in longitudinal 
section, the " wall ” between two corallites is made of two opposed septal 
ridges. 
The tabulae are for the most part complete and fairly straight, but 
there is some variation in this as in the number, which, how^ever, is usually 
about 15 in 10 mm. They may pass from one corallite to the next straight 
through a pore. The constant sharp upturning of tabulae at the margins 
of the corallite, characteristic of C. canadensis var. antic ostiensis, is not 
found in this species. 
