MADREPORARIA OF THE BOULONNAIS. 709 
In a genus which, like Montlivaltiia, contains a great many 
species, it is most important, if only for their proper determi- 
nation, that the appearances exhibited at different periods of 
‘their growth should be carefully examined and well understood. 
And this applies more especially to a comparison of the respective 
periods of growth of such species as are broadly attached and those 
which are fixed by a point, as well as to the elongated fossula of 
others, as compared with the same part in those in which it is 
circular. 
The earliest period of growth of some Montlivaliiw, when nothing 
more than a superficial and attached star-like form is visible, pre- 
sents the appearance of several rings, one within the other. These 
are nothing more than successively developed walls. Within the 
inner circle are the earliest or primary septa; in the second and 
other succeeding circles are the second and successively produced 
cycles, which, as well as the primary ones, take their growth in 
anticipation of the encircling walls. However, it not unfrequently 
happens, that more than one cycle is produced before the growth of 
the enclosing wall commences. Very beautiful illustrations of this 
may often be seen attached to some hard substance, such as a shell, 
which have not yet attained to any appreciable height, but present, 
in their periods of expanding growth, much the aspect of a section 
of an exogenous tree, the rings of growth and medullary rays being 
represented by the walls and septaof the coral. A very interesting 
instance of this is shown in a very young and attached example of 
Monilivaliia Victorie in the collection of my friend Mr. Beesley, of 
Banbury. More instructive still are the under or attached surfaces 
of certain Montlivaliie with broad bases from the Trigonia-grit of 
the Inferior Oolite near Cheltenham. When a fortunate detach- 
ment has laid the attached base of the coral open to view, it pre- 
sents all the periods of growth which took place until the corallum 
had attained to nearly its full diameter, and all the cycles of septa, 
and the successively formed and superseded walls, with the clearness 
of an explanatory diagram drawn on paper. 
Full-sized examples of the Montlivaltie just mentioned have a con- 
siderably elongated fossula; but the examination of the base shows 
that at first, and until several cycles of septa and several encircling 
walls had been produced, the fossula was represented by a mere 
point. It was not until the corallum grew in an upward direction, 
that the fossula lost its circular form, and became linear. 
But in other species, which are fixed by a point only, the diameter 
of the corallum is not so much the result of a series of successively 
produced walls, as of the expanding and upward growth of an early 
formed wall, which growth must of necessity in such species take 
place before the whole of the cycles are produced, instead of after- 
wards. There are other species, again, which are attached by a base 
of intermediate size. These will increase in size by both methods of 
growth. Both the turbinate and the cylindrical or intermediate forms 
may have the fossula circular or linear ; but from what has already 
been said, it will be readily understood that, when elongated, some 
Q.J.G.8. No. 160. | 3B 
