286 DESCRIPTION OF CHALK CORALS. 
50 to 75 degrees, and the distance between the successive bi-partitions from 
eight to three lines. The branches were almost constantly cylindrical, and only 
slight differences were perceptible in the diameter of mature, unaltered frag- 
ments, that of the greatest being about a line: in immature terminations it was 
three-quarters of a line, and in thickened, greatly altered portions a line and a 
quarter. 
Two upper extremities of a branch presenting a nearly perfect, young condition 
were observed. The finer (fig. 7a) exhibited an obtuse, round point ; and the whole 
surface to the very apex displayed well-formed projecting apertures, and when ex- 
amined in a lateral position, thin longitudinal lines were visible, between which 
could be detected rows of minute pores, but when vertically, only a reticulated 
structure was obvious. All the essential components of the coral’s fabric, how- 
ever, evidently existed as shown by the former mode of viewing the fragment. 
The surface of mature, unaltered, regularly formed branches (fig. 7b) was traversed 
by bold, longitudinal ribs, similar to those delineated by Herr Roemer (op. cit. 
tab. 5. fig. 29 b), and between them, occupying the whole breadth of the interval, 
occurred the tubular projecting mouths. The subordinate medial rib was most 
distinct when the branch was examined laterally, but it could be detected when 
in any position ranging generally from one aperture to the next; and on each 
side of it, a row of fine pores or indentations could be discovered with care. In 
fragments possibly a little older, the middle rib was stronger, and the pores more 
distinct. In consequence of numerous abnormal examples, some of which will 
be noticed presently, it was difficult to select specimens which actually gave a 
passage from an unthickened to a thickened state. Fig. 7c is however believed to 
represent a branch considerably altered. The apertures are much less prominent, 
exhibiting only a circle on a level with a surrounding porous structure, and they 
are often invisible, or their place is indicated by a small projection coated by the 
network : the longitudinal ribs are also similarly overlaid and in part concealed. 
In the lower portion of the specimen, the mature characters were even less ap- 
parent. Probably Herr Roemer’s figure 29 d was delineated from a fragment 
which had undergone an equivalent amount of change. Fully altered states 
(fig. 7c, c) displayed a surface wholly occupied by a fine reticulation, composed 
principally of limited rows of pores with very slender divisional lines. The point 
more immediately claiming attention in these aged conditions is the total oblitera- 
tion of the most prominent structures in mature stages, and the great develop- 
ment of one which in such circumstances is very subordinate. In the altered 
