SILURIAN FOSSILS 



61 



6. a 

 b 



7. a 

 b 



8. a 

 b 



9. a 

 b 



Well preserved apertures with a central ring and radiating ridges . . . Hallopora 

 No ring or radiating ridges in apertures Chilotrypa 



Colony without lace -like holes Fistulipora 



Colony with regularly arranged holes giving it a lacy appearance 8 



Holes narrower than the branches Clathropora 



Holes as wide as or wider than the branches 9 



Branches sharply keeled, crossbars short and wide Semicoscinium 



Branches angulated but not keeled, crossbars thin and narrow . . . .Fenestrellina 



Diamesopora (fig. 92) is twig-like and branching. It is unique in having hollow branches, 

 a character which is easily seen on the broken ends of branches. Two species are common in 

 the Niagaran. 



The next 5 genera have solid branches, that is, the tubes reach to the center of each 

 branch. 



Trematopora singularis (fig. 93) is distinguished by its monticules which 

 form a series of bumps on the surface of the branches. It is common in the Ni- 

 agaran. 



Eridotrypa echinata (fig. 94) has no monticules and its apertures are close - 

 set and polygonal. The walls of the apertures are noticeably thicker than in the 

 next species. It is common in the Niagaran. 



Monotrypella consimilis also lacks monticules and has polygonal apertures, 

 but their walls are thin. It is common in the Niagaran. 



In Hallopora elegantula (fig. 95) the apertures are widely spaced, there are 

 no monticules, unlike some of the Ordovician species, and in well preserved 

 specimens the apertures have a central ring with ridges radiating from 

 it. It is common in the Niagaran. 



Fig. 92 



v£cX6 



enlaced 



Fig. 95 



.-Jf-lu 



Chilotrypa varia is like Hallopora but its apertures 

 lack the central ring and ridges. It is common in the Ni- 

 agaran. 



The remaining genera are leaf -like. Fistulipora 

 neglecta is distinct from all the others in that it forms 

 irregular crusts on other objects. It is rare in the 

 Springfield and common in the Cedarville. 



Fig. 93 



The last three genera have fan-like or funnel-shaped col 

 onies (figs. 96-98) made up of a series of twig-like branches 

 joined by crossbars. The whole colony seems to be pierced 

 by little windows. 



In Clathropora alcicornis (fig. 96) the crossbars are ,as 

 wide as or wider than the windows and there are many cells 

 across each branch. It is common in the Niagaran. 



In Semicoscinium t enuiceps (fig. 97) each branch has a 

 sharp keel down the middle, the apertures are in 2 rows on 

 each branch, and the crossbars are short and wide. It is com- 

 mon in the Cedarville. 



If 



enlarged 



Fig. 96 



