BROWN, RUGOSE CORALS 
93 
but in its adult condition it is characterized by a new and distinctive feature, 
namely: the presence of carinse or lateral ridges on the sides of the septa. 
This line of development apparently becomes extinct after it gives rise to 
the compound form Heliophyllum confluens. Other species described as 
Heliophyllums, such as II. tenuiseptatum, apparently do not belong to this 
genetic series. An attempt was made to connect the latter species with this 
series, but it could not be done. In sections made from the very early stages 
of this species, no septa could be found. In the earliest stage in which septa 
were found they were all rather short and only extended a short distance 
from the wall into the calyx. 
Another line of development in this same period, and one characterized 
by a reversion to ancestral features coupled with a very specialized manner 
of growth, is represented by the genera Microcyclus and Hadrophyllum. 
The particular species studied was Hadrophyllum orhignyi, which in its 
development illustrated very well the early Streptelasma mode of arrange¬ 
ment and development of the septa followed by a very specialized short 
cushion-shaped growth of the calyx as a whole and the primitive pinnate 
arrangement of the septa within the calyx. 
Possibly there may have been other lines of development which branched 
off from the same ancestral stem during the Devonic, but the ones described 
above are the only ones which have been considered in this study. 
In the Devonic period the acme of development both of the rugose corals 
in general and of the Streptelasma group in particular is reached and passed. 
With the beginning of the Carbonic only a few terminal members of the 
various series are left and at the close of the Carbonic the whole group 
is extinct. 
Among the Mississippic and Carbonic forms closely related to and appar¬ 
ently directly derived from the Devonic forms discussed above are the 
two genera Lophophyllum and Hapsiphyllum. The genus Lophophyllum 
is apparently directly derived from Stereolasma, and the prominent pseudo- 
columella of the latter is even more emphasized in the former and is carried 
up in the calyx of the individual corallites above the point where the fully 
developed septa unite, and, attached only to the inner edge of the counter 
septum, it projects up into the open cup. Hapsiphyllum, on the other hand, 
is apparently derived from the Heterophrentis line. The cardinal fossula, 
which in Heterophrentis is a prominent character, is in this species so 
accentuated that it forms a true inner wall. A study of the development 
of H. calcareforme illustrates the change from the Heterophrentis stage to 
the primitive true inner wall stage, and the development of H. varsoviense 
carries the change still further and gives the very prominent inner wall 
condition. 
