312 DESCRIPTION OF CHALK CORALS. 
smooth, thickened surfaces with broad protuberances ; cells in the axis elongated 
downwards occupying wholly the central area, slightly and regularly inclined 
outwards ; in external additions range of cell limited, position very variable ; 
aperture arched at the distal extremity, sometimes nearly straight at the proximal 
end, margin not raised, position uniform in unthickened branches, very irregular 
in thickened ; operculum solid, surrounded by a furrow ; intermediate structure 
reticulated or porous. 
Ceriopora papularia, Michelin? Iconographie Zoophytologique, p. 124, pl. 32, 
Hew7e 
The fine specimen submitted to examination (fig. 6) consisted of numerous 
dislocated branches, but without a trace of a base. It was five inches in one di- 
rection, two in another, and nearly three in the third. The branches diverged gene- 
rally at a considerable angle, and occasionally anastomosed. The longest frag- 
ment measured 3+ inches, and presented two bifurcations. ‘The mode of branch- 
ing appeared to be almost invariably by terminal subdivisions, and not by lateral 
shoots ; the plane of divergence, to the extent ascertained, was also nearly simi- 
lar in successive partitions. ‘The measured axeal branches did not exceed a line 
in diameter ; while the corresponding dimension of the most thickened was three 
lines, every intermediate breadth occurring in the specimen. It was not possible 
to reduce the increments to regular concentric layers, though transverse sections 
gave sometimes the semblance of such an arrangement: even in those cases, 
however, the circle was never complete ; and in vertical sections, the greatest 
irregularity was manifest (fig.6e, f). There was nevertheless what might be termed 
successive levelings, effected apparently by the intermediate structure. Pur- 
posely worn-down specimens often exhibited a seemingly partial absence of 
visceral cavities, but this character was conceived to be due in part to unequal 
mineralization. Operculated or solidly closed apertures would necessarily pre- 
sent great impediments to infiltration, and the cavities thus provided would be 
less liable to a complete filling up than those not similarly guarded. In one 
case, the calcareous matter carried inwards by water through the textile pores 
would afford only pure crystallizable carbonate of lime; whereas in the other, 
the open apertures would admit particles of chalk, which by aid of the crystal- 
line matter would assume a character very like that of the solid portions of the 
coral. Only one instance of what was regarded the termination of a branch de- 
prived of vitality during development was noticed. It was worn, but presented 
an obtuse cone, the apex of which consisted of numerous minute tubuli, the com- 
