DESCRIPTION OF CHALK CORALS. 301 
apparently half a line. The contour was nearly uniform from the lower to the 
upper extremity, but neither termination was perfect ; and the slightly convex 
surface was confined to the region occupied by the visceral cavities, arising solely 
from their existence, the marginal bands being very thin and flat. Of the 
general habits of growth no opinion can be offered. The number of apertures in 
a transverse row, including both the curves, varied from six to nine, smaller 
series prevailing in the lower portion of the specimen, and greater towards the 
upper extremity, but without any change of distribution indicative of a bifurca- 
tion: the number of apertures in opposite arcs was also often dissimilar, omitting 
from the calculation the central opening, the defect being generally towards the 
observer’s right, or if that mouth were included to equalize the enumeration, 
then the opposite curves were unsymmetrical in position, but without becoming 
alternate. The series forming the direct centre was arranged nearly in a straight 
line, but those on the sides quincuncially. The margin was equally raised and 
sharp throughout the specimen, proving no surface-change with respect to that 
structure, so far as the amount of evidence was concerned, the inner area of the 
mouth being likewise invariably open. The tubuli constituting the general sur- 
face-layer were defined by translucent lines in general very distinct, except near 
the lower extremity of the coral, where a slight thickening had apparently taken 
place. That the narrow opake intervals between those lines were hollow was 
clearly shown in the fractured section (fig. 2a); also near the upper extremity of 
figure 2*, a defective portion exhibited a congeries of minute, obliquely penetra- 
ting openings, which viewed in some directions bore the semblance of cells ; 
and in other parts, where the distance between the apertures was small, the lines 
formed a fine reticulation, which might also be regarded, if considered alone, as 
marking a cellular composition ; on the contrary, whenever the polype had ample 
space for development, especially in the lateral bands, the interval between the 
lines was so greatly elongated as far to exceed the dimensions ordinarily assigned 
to a cell. In the immediate centre the tubuli ranged vertically, but elsewhere 
more or less outwardly, though always nearly coincident with the direction of 
the visceral tubes. The breadth was for the greater part much less than the 
diameter of the apertures to the abdominal cavities, varying however consider- 
ably, and being often unequal in an individual example: the greatest uniformity 
occurred in the side bands. The layer constituting the general surface had 
commonly a single series of these minute hollows, disposed horizontally, but in 
the depressions between the visceral tubes was an inferior row to fill up the in- 
2Rk 
