to Micro-Palwontology. 293 
ened (fig. 3, B) ; and they sometimes exhibit a sort of periodic 
variation in the amount of this thickening, causing the walls 
to be thicker in some parts than in others. In no case, how- 
ever, does the wall come to consist of a series of unthickened 
segments separated by thickened annular nodes; so that 
neither in rough fractures nor in longitudinal sections do we 
find the walls of the corallites exhibiting a moniliform or 
beaded aspect. 
This last point brings us to consider for a moment the 
generic position of this species. ‘There can be no doubt that 
in its general characters, Monticulipora? tumida, Phill., makes 
a very close approach to such species of Stenopora as S. tas- 
maniensis, Lonsd., and, still more, S. Hows, Nich. This 
was formerly pointed out by myself; and, after a renewed 
investigation, I can only repeat that “so far as our present 
knowledge goes, the only points which would definitely sepa- 
rate M. tumida, Phill., from Stenopora are, that it certainly 
shows no traces of the peculiar moniliform and periodic thick- 
ening of the walls of the corallites which is characteristic of 
the latter genus, and that there is no evidence as to the pre- 
sence of mural pores” (‘The Genus Monticulipora,’ p. 124). 
The existence or non-existence of mural pores may be left out 
of account, however, as these structures are so difficult of de- 
tection; so that the structure of the wall alone remains to 
separate MW. tumida from Stenopora. It must be added, how- 
ever, that this last point is one so essentially characteristic of 
the genus Stenopora, Lonsd., that it would seem impossible 
to include under this name any type which did not exhibit 
this peculiar feature as regards the mature corallites. 
The species from which it is most difficult to separate M. ? 
tumida is Stenopora Howsii, and I may briefly summarize 
the chief points which distinguish them. 
(a) Dimensions of corallum.—The corallum of M.? tumida 
is in general markedly smaller than that of S. Howsz/, branches 
of the former being most commonly about a line and a half or 
two lines in diameter, whereas the stems of the latter average 
about four lines in diameter. Still, large stems of .? tumida 
cannot by this character alone be separated from small stems 
of S. Howsit. 
(6) The calices of M.? tumida are markedly thickened and 
usually circular or oval, whereas those of S, Howsii are com- 
paratively thin-walled and are generally polygonal. 
(c) The lips of the calices in M.? tumida carry numerous 
blunt spines, which in well-preserved specimens terminate in 
minute circular apertures, and which give to the surface a 
markedly rough and spinulose aspect. In S. Howsii, though 
