288 Dr. H. A. Nicholson’s Contributions 
polygonal lines of demarcation of the different corallites ; but 
even in this case such lines only appear as clear spaces (Pl. 
X. fig. 6). In the structure of the wall, therefore, S. Hows? 
agrees with such forms as Stenopora tasmaniensis, Lonsd., 
and differs from such as 8, ovata, Lonsd., and S. crinita, 
Lonsd., the boundary-lines in these latter species remaining 
permanently recognizable as distinct dark lines marking off 
the originally polygonal corallites *. 
The tabule of the peripheral region of the corallum are 
exceedingly characteristic, the great majority (possibly all) 
being perforated by a central oval, or subcircular, or reniform 
aperture, the structure, however, being wholly unlike that 
which characterizes the genus Prasopora, Nich. & Eth. As 
seen in tangential sections (Pl. X. figs. 4, 7, and 8) the 
tabulee appear as circular ledges, surrounding the visceral cham- 
bers, and each perforated by a central aperture, the immediate 
margin of which is somewhat thickened. As seen, on the other 
hand, in longitudinal or transverse sections (PI. X. figs. 9 & 10), 
the tabule present themselves as so many pairs of short, nearly 
horizontal, or somewhat deflexed processes, the free ends of 
which, where they abut upon the central aperture, are slightly 
thickened or bulbous. Some of the tabule: appear to be com- 
plete and to pass completely across the visceral chambers of 
the corallites. It is probable, however, that all the tabule: in 
the peripheral region are really perforated, and that the 
apparent completeness of some of them is merely due to the 
fact that the line of section at that particular pomt traversed 
the visceral chambers excentrically, and therefore did not pass 
through the central perforations of the tabule. In any case, 
the tabula mostly spring from the unthickened segments of 
the corallites, and are mostly about 4, inch apart. It is 
also the last-formed tabula which appears as the perforated 
diaphragm at the bottom of so many of the calices. 
Finally, in tangential sections the appearances presented 
vary according as the section passes through the tubes at the 
level of their thickened nodes, or at that of the unthickened 
internodes, the resulting differences being usually observable 
in different portions of the same slice. Thus, if the section 
should traverse the unthickened segments of the corallites (as 
seen in the lower part of fig. 1, A, and in Pl. X. figs. 4 and 
5), the tubes appear to be comparatively thin-walled and ap- 
proximately polygonal, and there are comparatively few and 
“ The occurrence of such a well-marked difference of structure as that 
above noted, in species otherwise so closely allied, would lead us to sup- 
pose that it is, perhaps, hazardous to lay great stress upon the amalga- 
mation “or non-amalgamation of the walls of the corallites as a point of 
generic distinction, 
