BROWN, RUGOSE CORALS 
77 
broken at the edge, three or four carinae are clearly indicated on each of the 
septa. 
Figure 21f is cut from near the base of the cup in an adult corallite. It 
shows clearly the primary and secondary septa alternating with the tertiary 
septa, which in this stage are nearly as long as the former. The septa of 
all three series have a considerable number of carinse, and it is clearly seen 
that the carinae near the center are stronger and heavier than those near the 
margin of the section. This is due to the fact that the carinae near the 
Fig. 21. Heliophyllum halli. 
center are the first to arise, while new ones are added between the margin and 
those already present. 
From the foregoing developmental study of the morphology of even such a 
distinct and specialized species as Heliophyllum halli, it is seen that in its 
younger stages it is only a Streptelasma and that the specialized characters 
are only later additions as the individuals approach their adult condition. 
Heliophyllum halli apparently gives rise to the compound form Heliophyllum 
confluens of the Hamilton, and then the line dies out. Heliophyllum tenui- 
