258 DESCRIPTION OF CHALK CORALS. 
not deep, sides steep, with about nine indentations ; general surface modified by 
age and thickened, the additions concealing the intervals. 
Figure 29 fully represents, in the natural size, the general characters of the 
coral; and the fine specimen from which it was taken afforded perhaps sufficient 
evidence of every important condition of growth. The portion given on an 
enlarged scale (fig. 30) exhibits equally well the nature of the furrows or ribs, 
the characters of the abdominal cavities, and the relative position of the articular 
surfaces. The specimen delineated in figure 33 was believed to be a root of 
Axogaster cretacea ; and the transverse division at the lower extremity of figure 30 
presents a somewhat similar appearance, but it is believed to be only a contorted 
ramification, the surface being rounded on the under side, and not compressed 
as in the root (fig. 33). The downward increase in size was gradual, where the 
growth had not been greatly affected (the portion, figure 30, which measured 14 
inch in length, was at the upper end one line broad, and at the lower two), but 
occasionally globular protuberances occurred with minor irregularities. The ex- 
tremity of a growing segment was slender and conical, but it displayed a furrowed 
surface to the very apex and abdominal cavities a little below it. No true branches 
or divergences in the segments, similar to those in Isis Hippuris, were noticed ; the 
closely applied lateral shoots (fig. 30) being clearly side segments, as they were 
separated from the parent stem by a circular line, with a want of perfect coin- 
cidence in the range of the furrows ; while a divergence in the recent coral has no 
partition interval, and the ribs and furrows are uninterruptedly continued. The 
grooved pits occasionally visible in the side of the stems (fig. 32), and structurally 
identical with articular surfaces, afford further evidence of the assigned nature 
of these lateral shoots. The segments varied in length from one to ten lines, 
the greater extension not being due to overlaid additions concealing intervals. 
The surface in young and mature states was strongly ribbed, with intermediate 
furrows of rather less width ; and the ribs were rounded and waved in their lon- 
gitudinal range bending around the visceral cavities. At the junction of the 
closely applied lateral nodes, a want of perfect conformity in direction was appa- 
rent on the side of the offset ; but more or less of continuous range was visible 
on the upper and under surfaces. Proceeding downwards from young to older 
portions, the ribs became gradually less prominent, and the furrows shallower ; 
while in aged segments the surface displayed only irregular striae. The articular 
extremities varied in the degree of convexity and concavity ; but the fully shown 
displayed a central boss (fig. 30 a) or a corresponding depression. The circular 
