The Use of Graphs in Paleontology. 403 
3a. Zaphrentis delanouer. 6a. Zaphrentis disjuncta (early). 
4a. A parellela. Ta. x by (typical). 
5a, hi constricta. 8a. 35 a (advanced), 
The changes measured were as follows :— 
A. The reduction of the fossulee. 
B. The length of the cardinal fossule from the epitheca to central 
stereom, or when this has disappeared, to the inner end of the 
counter cardinal septum. This is expressed as a percentage of the 
diameter. 
C. The width of the fossula at its inner end, expressed as a per- 
centage of the diameter. 
D. The distance between the inner ends of the alar septa, 
expressed as a percentage of the diameter. This reflects the pro- 
gressive shortening of the septa and their withdrawal from the 
centre. 
__E. The percentage length of the shortest septum in the cardinal 
quadrants (cf. Fig. 7a). 
Ff. The percentage length of the shortest septa in the counter- 
cardinal quadrants (Fig. 7). 
G. The reduction of the central stereom. 
H. The percentage of free septa. 
Measurements E to H call for further explanation. 
Taking E and F first, at stage 3 (Fig. 9), the septa still exhibit 
a markedly pinnate arrangement. During the succeeding stages 
the shortest septum in each quadrant, viz. those which lie next to 
the cardinal and alar septa on the counter-cardinal side (Figs. 7a, f) 
undergo striking changes which reflect two important alterations 
affecting the coral as a whole. 
The first or earlier alteration is the passage from a pinnate to a 
radial symmetry. Whilst this is taking place the short septa elongate 
until they are equal in length with the other septa. 
The second and later alteration takes place when an advanced 
stage in the attainment of a radial symmetry has been reached. 
All the septa now begin to shorten and to withdraw simultaneously 
from the centre. This change is also shared by the four septa under 
consideration. 
These four septa thus elongate during the earlier stages 
and shorten during the later stages of evolution. This reversal 
in the direction of change of these septa is most simply expressed 
in graphic form by placing the point of reversal on the zero line, and 
representing the changes which precede it below and those which 
follow above the line. 
Turning now to G and H, in stage 3 (Fig. 9), there is a considerable 
deposit of stereom at the centre of the coral, which binds the inner 
ends of the septa together. With the progress of evolution the 
stereom becomes reduced in quantity and the septa gradually 
become liberated. This change can be expressed either in the form 
of a series of diagrams representing the reduction of the area of the 
stereom (G), or by figures giving the percentage of free septa (H). 
