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ANNALS NEW YORK ACADEMY OF SCIENCES 
stem gives rise to numerous widely diverging lines which rapidly develop 
and specialize along some particular line, some progressive and some retro¬ 
gressive, and then terminate and disappear. The development of this group 
of corals can best be compared to the flight of a sky rocket. It starts from 
the ground with a sputtering, throwing out a few sparks, then shoots upward 
through the air with a straight or slightly wavering course and with perhaps 
an occasional flicker until a certain height is reached, when suddenly it 
bursts and throws out sparks in all directions, some up, some down and 
some horizontally. 
At the end of the lower Devonic comes the bursting stage in the Strep- 
telasma line. This single genetic series now seems to give rise to diversified 
groups which branch out in all directions, some lines advancing in a pro¬ 
gressive way but in different directions, while others seem to retrogress and 
return to a condition somewhat similar to ancestral stages but distinctly 
marked as degenerate series. 
During the lower Devonic or Lower Helderberg period, the Streptelasma 
line of development is represented by Enterolasma strictum. This is very 
similar to the representatives of the same genus from the Siluric but is char¬ 
acterized by a somewhat more solid and substantial pseudocolumella and 
by the union of the tertiary septa with the adjacent primary and secondary 
septa at their inner margin. 
With the middle Devonic, the rapid divergence of the various lines of 
development begins. The line of development representing the appar¬ 
ently most direct continuation of the Streptelasma line is that represented by 
Stereolasma rectum, occurring most abundantly in the Hamilton shales. 
This species differs from Enterolasma strictum only in the fact that it has a 
complete and solid pseudocolumella reinforced by a deposit of stereoplasm 
between the septa and near the pseudocolumella. 
Closely related to these Streptelasma forms and either derived directly 
from them or coming from [ Zaphrentis ] racinensis of the upper Siluric (which 
in turn is derived from the Streptelasma stem) are a group of Zaphrentids 
found abundantly in the Onondaga limestone. Heterophrentis prolifica is 
typical of this group. It represents a line in which the emphasis of develop¬ 
ment falls upon the cardinal fossula rather than upon the pseudocolumella 
as is the case with Stereolasma rectum. Other closely related and congenetic 
species are II. multilamellosa, H. wortheni and II. edwardsi, all from the 
Onondaga beds. 
Arising from the Streptelasma stem at about the same time and closely 
paralleling in its early development Stereolasma rectum, the species Helio- 
phyllum halli represents another divergent line of development. During 
its early development this species cannot be distinguished from S. rectum, 
