46 Dr. H. A. Nicholson on the Minute Structure 
lum ; and its floor may be flat, or may exhibit a small rounded 
eminence formed by the primary septa. The principal feature 
of importance presented by the calice is, that the free edges 
of the septa are invariably furnished with prominent spines, 
formed by the terminations of the ascending dissepiments. 
> 
1) 
V4 

A, cross section of Heliophyllum Halli, E. & H., of the natural size, 
showing the manner in which the septa are continued to the centre, 
and showing the arched ascending dissepiments, but having the other 
dissepiments omitted. B, vertical section of H. Halli, showing the 
central tabulate area, and both the ascending and descending series of 
dissepiments. OC, cross section of Crepidophylhun subcespitosum, the 
descending series of dissepiments being, as before, omitted: twice the 
natural size. D and E, cross sections of the same species, of the 
natural size. (D shows the central tabulate area completely closed 
in by the central tube; and E exhibits the cut edges of some of the 
delicate descending series of dissepiments.) IF, vertical section of a 
fragment of the same species, twice the natural size, showing the 
central tabulate area, with its enveloping wall, and the ascending and 
descending sets of dissepiments. J is slightly generalized, and 
some details have been omitted. All the specimens are from the 
Hamilton group of the State of New York and of Ontario. 
The internal structure of the corallum in Heliophyllum is 
somewhat complex, but is rendered readily intelligible by 
means of transverse and longitudinal sections. The tabule 
