On Streptelasma Profundnm. — Sardeson. 289 
and as Kunth tell? of Tetracoralla in general, the four points 
of septal increase do not exactly keep even. The four quar- 
ters into which the circle of septa isdivisible, coinciding with 
the four primary septa, rarely each contain an equal number. 
In this species the counter or anterior quarters have 5 to 10 
per cent, the greater number, but correspondingl}^ right and 
left quarters are on an average equal, although notrarel}^ un- 
equal. Consequently one need not expect the whole number 
of septa which is about 120 to be constant. 
Incre^ise in the number of septa appears to always cease 
when the corallum has expanded to nearly its greatest diam- 
eter (see fig. 1, pi. XVI) and the long specimens have no in- 
crease of septa in that part which I have designated for con- 
venience the senile growth, butonly in tlie expanding portion. 
The closeness of the septa to each other varies considera- 
bly. In early growth tliree septa occur in the space of Imni., 
in raaturer growth on an average two or less or even one to 
1mm. occur. In rapidly expanding cells or in rapidly expand- 
ing portion of a cell the septa are widest apart. A constric- 
tion in circumference does not as fiir as observed ever reduce 
the number of septa but only the space between them or their 
thiclcness or both are contracted. Quite evidently the varia- 
tion in coarseness of septa was determined by accident of 
growth like the rate of expansion of the cell which has been 
already described. Local conditions might therefore have 
produced a distinct phase of development such as uniform 
coarseness of the septa but no such character has been found 
to prevail in any set of fossils of one locality and horizon, al- 
though the average seems to vary in ditt'erent sets to a certain 
degree. 
The septa unite in the middle of the cell at the bottom of 
the calycle and are more or less "twisted together." In the 
attached portion of the apices the septa may be irregular but 
later they become regular. Soon they become "twisted" or 
irregularly bent and more or less irregularly shaped tabulae 
unite with them in a confused manner. A section across the 
base of the cell opening in a normal young specimen shows 
however very clearly the regular order of their union at that 
iBtage(fig, 7, pi. XVI), and the "twisting together" of the septa 
later does not represent a ditt'erent order of arrangement but 
