62 
The average diameter of the corallites is about half a millimetre ; they 
are polygonal in the peripheral region, basaltiform in the axial portion, and 
possibly not in close contact thronghont. The external aspect of the corallites 
in fractured specimens is very characteristic. The first point to strike the 
eye is the basaltiform outline, with the gradual appearance of crennlations, 
or moniliform swellings, as the upper surface of each successive stratum or 
colony is approached (PI. II, Pigs. 1 and 2) . This applies to the tubes whether 
in the peripheral or axial region, it being a mistake to suppose that these are 
confined in a greater degree to the former area. In the axial region, 
however, the annulations are not seen in the central portion of an internode, 
hut only at the final period of growth, hut generally when the internodcs 
arc long the annulations are single, as originally figured by Lonsdale, or at 
the most two or three. At the terminal stage in each colony, like those in 
the peri|^heral area, they become closely contiguous, and are specially 
numerous when the strata are short. In PL V, Pig. 3, are represented two 
corallites, viewed from the interior, in which the thickened ring, giving rise 
to a moniliform expansion, is plainly visible. 
The primordial wall, or test, must have been very thin, shelling off in 
our fractured specimens as a thin pellicle. 
As already explained in the generic description, the tubes do not 
appear to have been in absolute contact throughout, hut a very thin space 
seems to exist between them. In PI. V, Pig. I, this is illustrated, the black 
central infilling between contiguous corallites being the separating medium, 
hounded by the lighter-coloured walls of the tubes, and the cavities of the 
latter again filled with darker matrix. 
Xo better illustration of the variability in the thickness of the walls 
in Stenopora can he afforded than in the structure of the present species. 
Here the width of the walls varies according as the plane of the section 
corresponds with the thickened nodes, or traverses the unthickened inter- 
nodes. In PL VI, Pig. 4, the abrupt passage from one to the other is clearly 
shown, hut in many specimens the entire absence of nodes is a marked 
feature. In the majority of examples of S. criuita the thin proper walls of 
the corallites are usually liued by a continuous investment of calcareous 
substance, in this particular instance brown, of variable hut usually consider- 
able thickness. This investment is so invariably present, is so constant within 
