*146 THE CANADIAN NATURALIST. [Yol. Vll.. 



'2. The septa in H. exiguum exhibit on their flat sides " about 

 six obscure arched s^?'i<:c to one line." Those of i'. i/o^«?ii ex- 

 hibit a succession of arched grooves of considerable depth, sepa- 

 rated by somewhat tumid interspaces; and these grooves are 

 only about four or five in the space of one line. Nor can it be 

 supposed that this discrepancy is due to any confusion on my 

 part between casts of P. Logani and the actual coral itself, . 

 such a mistake being impossible in dealing with the well-preserved, 

 specimens of the Corniferous formation. 



3. The septa in P. Logani bifurcate regularly in proceeding: 

 fjom the base to the cup, thus being always arranged in pairs in. 

 the upper part of the coral; whilst no such arrangement is stated. 

 as regards H. exiguum. 



4. When looked at as seen in transverse sections of the cup,.. 

 the septa of H. exiguum are seen to possess plain sides, as is the- 

 case in Zajjhrentis ; whilst those of P. Logani are denticulated 

 "with tooth-like dissepiments or spines, which rarely extend to the 

 contiguous septum. It need hardly be said that the structures 

 here alluded to are not to be confounded with the spines which 

 occur on the free edges of the septa of H. exiguum^ as in the 

 genus HeliophyUum in general. 



5. The epitheca of H. exiguum is thick, deeply annulated, 

 hardly showing the lines of the septa, and co-extensive with the 

 outer surface of the coral. In P. Logani ^ on the other hand,, 

 the epitheca is very slightly marked with ridges of growth, 'usually 

 exhibits distinct costae, and never appears to extend to the mar- 

 gin of the calice ; though it is certainly difiicult to say positively 

 whether this last 'appearance is natural of is due to a partial de- 

 cortication of the coral. 



Upon the whole, I think that the fossil here' described as 

 Petraia Logani is distinct from previously known forms. Its 

 reterence to Petraia is provisional, but it apparently cannot be 

 referred under any circumstances to the genus HeliophyUum.. 

 I have named it in honour of the eminent geologist, Sir William 

 Logan, F.R.S. 



Locality and formation. — Not uncommon in the Corniferous 

 Limestone of llama's Farm, Port Colborne. 



V. Alecto (?) Canadensis, n. sp. 



Polyzoaryadnate, attached parasitically to the exterior of corals, 

 branching in an irregularly dichotomous manner. Cells in realitjr 



