29 
23. HELIOPHYLLUM EXIGUUM (Billings). 
Heliophyllum exigwum (Billings), Canadian Jour. New Series, Vol. V. p. 261. Figs. 9° 
& 10. . 
“ Small, turbinate, more or less curved, often flattened on the side of the convex ecurva- 
ture ; radiating septa between sixty and eighty ; about six obscure arched striz to one line 
on their’ flat sides, and the same number of spines on their edges. The depth of the cup is 
equal to one fourth or one third of the whole length of the coral. In small specimens, the 
margin of the cup is thin and sharp ; but in large. ones rounded, and one line or a little more 
in width. About one half of the radiating septa reach the centre, and form asmall rounded 
elevation on the bottom of the cup. There is a septal fossette on one side, which, in all the 
specimens I have seen, reaches the centre. The surface exhibits a few sharp constrictions of 
growth, with rounded annulations between them, the latter often abruptly terminated on their 
upper sides. In very perfect specimens, fine encircling strize of varidble size, apparently from 
eight to fifteen in the width of one line. The horizontal str le, which indicate the number of” 
septa, are distinctly visible but not strongly marked. The position of the septal fossette is 
indicated on the outside of the cup by two septal ridges which extend the whole length of the 
coral, and constitute one of the lines along which the younger septa were added from time to 
time. 
“The greater number of the specimens are from six to nine lines in length, but some are 
full one inc’ The width of the cup is always a little less than the length of the entire fossil. 
The most common number of septa is sixty. The arched strize and spines are not often pre- 
- served” (Billings). 
I have been thus particular in quoting the description given by Mr. Billings of this 
species at full length, as in studying it, [ have met with great difficulties, which I cannot yet 
entirely explain. The few examples which I collected at Rama’s Farm, Port Colborne, (the 
locality given by Mr. Billings), that [ should be disposed to refer to this species, exhibit only 
the form of the corallum, the epitheca, and the edge of the calice ; and the characters of these 
are sufficiently distinctive, so far at any rate, as the other Canadian species of Heliophylinm 
are concerned. ‘The coral is small and turbinate, and is distinctly flattened along its convex 
curvature ; the epitheca is thick and continuous, and is thrown into strong enciicling ridges 
and annulations of growth, the vertical lines indicating the septa being very faintly marked, 
and the septa are alternately large and small, and are no denticulated on their flat sides, 
One perfect specimen .only (Fig. 6) have I obtained, showing all the internal characters, 
from the Corniferous Limestone of Hagersville; and this shows conclusively the distinctness 
of H. exiquum as a separate species of Heliophyllum. This specimen is small, turbinate, with 
a constricted pedunculate base, the longest side being flattened. The total length along the 
longest side is eight lines, on the shortest side four lines, the diameter of the calice being 
seven lines. The calice is distinctly quadrangular, moderately deep, with thickened margins, 
and a very well marked septal fosette. The septa are sixty-four in number, alternately large 
and small, with about five arched strie on their flat sides and the same number of short spines 
on their edges, The septal fossule corresponds with two primary septa, which extend the 
whole length of the coral, and from the two sides of which the other septa diverge; a pecu- 
liarity which I have failed to observe in the ex: unples from Port Colborne. The epitheca 
shows vertical septal strize, and encircling annulations of growth. 
Accompanying the specimens of HZ. exiguwm ( Bill- 
ings), at Port Colborne, I have found a large number of 
specimens which agree in some striking characters with 
HH. exiguum, but which differ from this species in other 
characters equally striking—and that to such an extent 
that I do not see how they can be referred to the genus 
Heliophyllum at all, seeming rather to belong to the 
genus Petraia. The discrepancies of observation indi- 
é cated here, I do not pretend to reconcile; but I shall 
Bigs: provisionally describe the specimens in question as dis- 
ee eg em epee) Cxleos view) tinct, under the name of Petruia Logan. 
showing the calice; b, Dorsal view of the same. 
Corniferous Limestone, Hagersville. 
