OF CENTRAL CANADA PART IV. 



233 



Favistella is identical or closely allied, but with longer septa, none 

 of which however reach the centre of the cell. (2), Amplexus, Fig. 

 143, mostly with simple corallum, in the form of a round, often more 

 or less contorted tube, bordered with short septa and divided trans- 

 versely by horizontal tabulae. (3), Zaphrentis, (Fig. 144,) a genus 

 of common occurrence in our Devonian strata, in simple horn-like 

 forms with well-developed radiating septa, and a septal fosse tte. 

 One species, Z. gigantea is of comparatively large size, but the 

 smaller species Z. prolifica, figured below, is more abundant. In 

 both, the septa reach the centre of the cup. Streptelasma, a 

 Silurian genus, is of very similar conformation, but some of its 

 septa form in the centre of the cup a kind of twisted axis or 

 " pseudo-columella." 



FIG. 142. 



Columnaria alveolata 

 (Goldfuss) Black River 

 (Trenton) Formation. 



FIG. 143. 



Amplexus laxatus (Billings). 

 Devonian. 



FIG. 144. 

 Zaphrentis prolifica (Bill- 



ings). Devonian. 



3. Vesiculo-Stellata : Tabulse confined to central or inner part 

 of cell, the outer part filled with vesicular tissue. Radiating septa 

 always present. 



This section includes a large number of both simple and com- 

 pound forms, belonging in part to somewhat ill-defined genera. 

 The more common examples of Canadian occurrence, comprise : (1) 

 Gyathophyllum, simple and compound, septa with smooth sides and 

 edges; (2) Heliophyllum, Fig. 145, like Cyathophyllum, but with 

 ridges or projections on the sides of the septa ; (3) Clisiophyllum, 

 simple, horn shaped, with conical elevation in centre of the cup or 

 cell,* and (4), Phillipsastrea, Fig. 146, compound, astrseiform, with 

 radiating septa prolonged beyond the outer walls of the cells. 



* A vertical section shews in Clisiophyllum three areas : a central area indicated by the 

 raised ends of the united septa ; an outer or marginal area of fine vesicular tissue ; and an in- 

 termediate area represented by more or less irregular tabulae or diaphragms. 



