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ANNALS NEW YORK ACADEMY OF SCIENCES 
I. Introduction and Historical Sketch. 
Although the rugose corals have been known and studied for more than 
a century, it was not until very recently that the fundamental principles of 
their structure and mode of development were understood. Kunth, in 
1869, first stated the law which governs the arrangement of septa in the 
majority of rugose corals, namely the appearance of main or cardinal and 
counter septa in one diameter of the calyx, and of two alar septa in the cross 
diameter; and the appearance of additional “pairs” of septa on either side 
of the main septum and on the remote side of each of the alar septa. 
The morphological structure and method of development of these corals 
was clearly grasped by the late Carl Rominger, as is evident from the follow¬ 
ing quotation from his treatise on the corals of the Lower Peninsula of 
Michigan, published in 1876. 1 
! The radial plications of the zoantharia rugosa are arranged in four primary 
fascicles, separated from each other by more or less conspicuous gaps. These 
fascicles, apparently segments of a cycle of rays, are in reality bilaterally situated 
in symmetrical position on an axial line, dividing the apparent cycle in two halves. 
The two fascicles on one side are equivalent to those of the opposite side, but differ 
from one another. For better illustration we may compare the circumference of 
a polyp cell to a horse shoe with narrow, almost closed aperture. Opposite this 
aperture, in the center of the curve, two fascicles meet with their equivalent sides, 
having an obscure narrow gap between them, the center of which often exhibits a 
solitary independent plication. This gap may, in distinction from the other gaps, 
be designated by the name of central gap. At the ends of these fascicles, remote 
from the central gap, and directed toward the aperture of the horse shoe, the pli¬ 
cations become gradually shorter, and, seen from the peripheral surface of the polyp 
cells, do not extend to the apex of the conical polyparium, but terminate above, 
nearer the calycinal margin. Another gap separates these shorter plications on each 
side from the adjoining fascicles of plications, which extend to the ends of the arms 
of the horse shoe. This pair of gaps is the lateral gaps. The further ends of this 
second pair of fascicles approach each other again, in the aperture of the horse shoe, 
leaving another larger gap between themselves than the other facicles, which may 
be termed the apertural gap ; its center is like the opposite obscure gap, occupied by 
a solitary plication. The plications of this second pair of fascicles are longest and 
extend to the apex of the polyparium on their end joining the lateral gaps, and 
shortest at the apertural gap. This is the order in the structure of all the polyp 
cells of the Zoantharia rugosa. If, during the progress of growth, new plications 
are added to the cycle of existing ones, the new ones are only inserted at those 
ends of the four fascicles which are directed toward the apertural gap, while the 
already existing plications are never disturbed by interposition of new ones, ex¬ 
cepting as indicated at the four ends of the fascicles, directed toward the apertural 
1 Paleontology of the Lower Peninsula of Michigan, Vol. Ill, pp. 92-95, 1876. 
