56 
ANNALS NEW YORK ACADEMY OF SCIENCES 
in the interseptal spaces in the same order as the secondary septa. They 
remain short and free throughout their length. They never appear to be 
attached by their inner margins to the adjacent secondary septa, as is the 
case in many species occurring in geologically higher horizons. 
Figures 1-5 represent five sectional views of five different individuals of 
different sizes and ages showing the different stages in development described 
above. Figure 1 has no septa. Figure 2 has the four primary septa and 
two pairs of secondary septa in the counter and cardinal quadrants. In 
figure 3, the secondary septa reach almost across the calyx, and in figure 4 
they are similar in arrangement to the adult shown in figure 6, while figure 5 
shows the first appearance of tertiary septa. 
In the limestones of the upper Ordovicic, particularly in the Cincinnati 
Group, are found an abundance of rugose corals which represent an ad¬ 
vance in the Streptelasma development. The most prominent among these 
are Streptelasma corniculum and Streptelasma rusticum. 
Streptelasma corniculum Hall. 
1847 Streptelasma cornicula Hall, Paleontology of New York, vol. I, p. 69, pi. 
XXY, la-e. 
1863 Petraia corniculum , Billings, Geology of Canada, p. 156, 938. 
1875 Streptelasma cornicula Nicholson, Paleontology of Ohio, vol. II, p. 218. 
This species, which occurs abundantly in the Trenton and Cincinnati 
limestones, is larger and more robust in growth than S. profundum. Hall 
( loc . cit.) describes it thus: 
Turbinate, curved near the base, which terminates in an acute point, some¬ 
what rapidly expanding above; cup profound; lamellse about sixty; surface 
marked by strong longitudinal lines indicating the lamellae, which are crossed by 
fine concentric wrinkled lines. Length varying from three-fourths to one and one- 
half inches. 
The septa in this species are more numerous, and in the later stages of 
growth are more nearly radially placed. The accompanying illustrations, 
figures 7-10, show characteristic stages in the individual development of 
the corals of this species. These are drawn from thin sections cut from a 
typical specimen. In figure 7, a section taken quite close to the tip of the 
coral, a condition is seen similar to the adult stage in S. profundum . The 
four primary septa are largest and most prominent, and the secondary septa 
are distinctly grouped in quadrants. Figure 8, at a later stage, shows a 
very similar arrangement. The secondary septa are more numerous, and 
more of them reach the center. In these two stages the septa are very thick, 
