31 



1. Heliophyllum exiguum, though this is not specially alluded to, must possess more or 

 less well developed tabulce ; but no* traces of such structures can be detected in P. Logani, in 

 longitudinal sections or in fractured specimens. 



2. The septa in H. exiguum exhibit on their flat sides " about six obscure arched strm 

 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 bifurcate 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 bifurcate. 



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. Logani are furnished with 

 strong tooth-like dissepiments or spines, which sometimes extend to the contiguous septum. 



5. T*he 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 Znphrentis 

 except that the septa are much less highly developed, and do not extend to the centre of the 

 coral, so that the tabulae 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 Coraiferous Limestone of 

 Ontario. 



25. AMPLEXUS YANDELLI (Edw. & H.). 



' f 



Amplexus Yandelli (Edwards & Haime). Pol. Foss. des Terr. Palfozoiques, p. 344, PL III. 

 Figs. 2, 2a. 



Amplexus Yandelli (Billings). Canadian Journal, New Series, Vol. IV., p. 123. 



Corallum simple, cylindrical, straight or curved. Calice varying in diameter from half 

 an 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 stri;e, 

 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 tabulae exposed over a large central area. The 

 tabulae appear to be generally flat ; and the septa have plain sides, and are alternately large 

 and small. 



Aiii/i/i'.i'/ix Yninl.Jli is not a common species in the Coruiferous Limestone, and does not 

 appear, so far as known, to occur at all in the Hamilton Group. As a 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. 



Lnrii/i/i/ ctnd Foriinti/on. Corniferous Limestone of Port Colborne. Also near Wood- 

 stock (Hillings). 



Genus DIPIIYPIIYLLUM (Lonsdale). 



< 'orallum simple, associated into large aggregations of long slender cylindrical flexnous 

 corallites, increasing by parietal or oalioinal gemmation, and placed usually at a -n- HIM- or 1 

 distance from one another. Internally a central area occupied solely by tabulffi, and usually 

 not encroached upon by the septa, with an exterior vesicular zone occupied by the septa. 

 No columella. 



