BROWN, RUGOSE CORALS 
73 
Septal striae, eight to ten near the base, and six to eight in the upper part, in a width 
of three lines. Septa from about one hundred to one hundred and twenty at the 
margin, where they are all rounded; most common number from one hundred to one 
hundred and ten. In general they alternate in size at the margin, the small ones 
becoming obsolete on approaching the bottom of the calyx, the large ones more 
elevated and sharp edged. The septal fossette is large and deep, of a pyriform shape, 
gradually enlarging from the outer wall inwards for one third or a little more of the 
diameter of the coral at the bottom of the calyx. Its inner extremity is usually 
broadly rounded, or sometimes straightish in the middle. It cuts off the inner edges 
of from eight to twelve of the principle septa, which may be seen descending into it 
to various depths. The surface layer of the bottom of the cup extends the whole 
w T idth, bending down a little near the margin as in Zaphreniis, and uniting with the 
inner wall of the cup all around. It thus seems to represent one of the tabulae of a 
Zaphrentis. 
This species occurs abundantly in the Onondaga limestone of the middle 
Devonic and is a typical representative of the Heterophrentis group. In 
its adult condition this is a slightly curved conical shaped coral with a very 
distinctly marked fossula in the position of the cardinal septum, and with 
the other septa slightly twisted at the center. In this condition it is very 
distinct from the Streptelasma forms, but when its developmental stages are 
studied it is found to be more closely related. 
In the accompanying figures are shown a few stages in the development 
of this form. Figure 20e is enlarged from a section sawed from the tip of a 
well preserved coral. It is almost identical with a slightly later stage in the 
development of a Streptelasma form. The four primary septa are most 
prominently developed and each extends to the center of the corallite. There 
are six secondary septa in each counter quadrant and five in each cardinal 
quadrant. Each secondary septum is attached by its inner margin to the 
next preceding septum. At this stage there is no indication of a fossula or 
any enlargement of the open spaces around the cardinal septum. If identi¬ 
fied from this section alone, the species would be classed under Stereolasma. 
In figure 20f a later stage of the development of the same individual is shown. 
Additional secondary septa have developed in the four quadrants. The 
cardinal septum is becoming shortened, and the position of the fossula is 
beginning to be indicated although not yet distinctly marked. In figure 20a, 
a section from another individual, giving a stage intermediate in develop¬ 
ment between the two above described, the septa are all shown to be normally 
developed except the cardinal. The cardinal septum, although still reaching 
to the center of the corallite, is much thinner and less prominent than the 
other septa. Evidently it is being retarded in its development. Figure 
20b, a later stage in the same individual, shows the cardinal septum no 
longer continuous to the center, and the fossula or open space occupying its 
