31 
1. Heliophyllum exiguum, though this is not specially alluded to, must possess more or 
less well developed tabude ; but no traces of such structures can be detected in P. Logani, in 
longitudinal sections or in fractured specimens. 
2. The septa in ZZ. exiguum exhibit on their flat sides “about six obscure arched strie 
to one line.” Those of P. Logani exhibit a succession of arched grooves of considerable width, 
separated by somewhat tumid interspaces ; and there are only about four-or five of these 
grooves in the space of one line. Nor does it appear possible that this discrepancy is due to 
any confusion on my part between casts of P. Logani and the actual coral itself, such a mistake 
seeming to be out of the question in dealing with the well-preserved specimens of the Corni- 
ferous Formation. 
3. The septa in P. Logani bifureate regularly in proceeding from the base to the cup, 
thus being always arranged in pairs in the upper part of the coral ; whilst those of H. exiguum 
are alternately large and small, and do not appear to bifureate. 
4. When looked at in transverse sections of the cup, the septa of H. exiguum appear to 
possess plain or but slightly denticulated sides, whilst those of P. Zogani are furnished with 
strong tooth-like dissepiments or spines, which sometimes extend to the contiguous septum. 
5. The septal ridges on the exterior of P. Logani are more strongly marked than in 
H. exiguum ; and the epitheca of the former rarely or never appears to extend to the margin 
of the calice, though it is certainly difficult to say positively whether this appearance is natural, 
or is due to the partial decortication of the coral. 
Upon the whole, I think that the fossil here described as Petraia Logani is distinct from 
previously described forms, and I do not see how it can, under any circumstances, be referred 
to the genus Heliophyllum. 
Locality and Formation.—Not uncommon in the Corniferous Limestone of Rama’s Farm, 
Port Colborne, and also at Hagersville. 
Genus AMPLEXUS (Sowerby). 
In this genus the corallum is simple, and in all essential respects similar to Zaphrent is 
except that the septa are much less highly developed, and do not extend to the centre of the 
coral, so that the tabulze are left exposed and free to view over a wide central area. The 
following is the only species which has as yet been detected in the Corniferous Limestone of 
Ontario. ’ 
25. AMPLEXUS YANDELLI (Edw. & H.). 
Amplexus Yandelli (Kdwards & Haime). Pol. Foss. des Terr. Paléozoiques, p. 344, Pl. III. 
Figs. 2, 2a. 
Amplecus Yandelli (Billings). Canadian Journal, New Series, Vol. IV., p. 123. 
Corallum simple, cylindrical, straight or curved. Calice varying in diameter from half 
ap inch up to an inch and a half.. Epitheca marked with from forty-five to sixty-five strong 
and angular septal ridges, which in well-preserved examples are crossed by fine encircling striz, 
and a few remote and regular folds of growth. The septa do not extend more than from half 
a line to two lines from the wall, leaving the tabula exposed over a large central area. The 
tabulze appear_to be generally flat ; and the septa have plain sides, and are alternately large 
and small. . 
Amplexus Yandelli is not a common species in the Corniferous Limestone, and does not 
appear, so far as known, to occur at all in the Hamilton Group. Asa rule, it may readily be 
recognised, even in fragmentary specimens, by the surface-characters, which are unlike those 
of any other of the simple corals of the Corniferous with which I am acquainted. 
Locality and Formation.—Corniferous Limestone of Port Colborne. Also near Wood- 
stock (Billings). 
Genus DipayPHYLLUM (Lonsdale). 
Corallum simple, associated into large aggregations of long slender cylindrical flexuous 
corallites, increasing by parietal or calicinal gemmation, and placed usually at a greater or less 
distance from one another. Internally a central area occupied solely by tabula, and usually 
not encroached upon by the septa, with an exterior vesicular zone occupied by the septa. 
No columella. 
