DEVONIAN FOSSILS 



79 



3. 



4. 



6. 



Key to the Commoner Devonian Bryozoa of Ohio 



( see p. 4 for use of keys ) 



Colonies twig-like, branching 2 



Colonies leaf-like 6 



Branches almost cylindrical 3 



Branches flattened 5 



Branches of almost the same diameter throughout 4 



Branches made up of short joints, the joints thickened 



at each end Helopora 



Branches about as thick as sewing thread (3/160 inch) Acanthoclema 



Branches twice as thick as sewing thread (3/80 inch) Streblotrypa 



Branching many times (like a twig with many leaves, 



see fig. 165) .Hederella 



Branching, but not as many times as Hederella (see fig. 166). Sulcoretepora 



Colony with regularly arranged holes, giving it a lacy appearance 7 



Colony without lace -like holes Fistulipora 



Colony made up of long rods joined by shorter 



cross-bars Fenestrellina, Semicoscinium 



Colony leaf -like, with widely spaced round holes Coscinium 



Helopora has a distinctly "jointed" appearance; the ends of the "joints" are thickened and 

 pointed at one end which fits into a socket in the next joint. _H. inexspectata is abundant in the 

 upper part of the Silica formation. 



Acanthoclema is stick-like, branching, but not jointed. It resembles Streblotrypa but 

 is smaller (3/160 inch in diameter) or about the size of stout sewing thread. A. ohioensis 

 is abundant in the upper beds of the Silica formation. 



Streblotrypa is like Acanthoclema but larger (3/80 inch in diameter) or about the size of 

 very fine twine. S_. anomala is abundant in the upper beds of the Silica formation. 



Hederella (fig. 165) is also stick-like but it forms a branching crust 

 on other objects. Figures 165 and 166 will distinguish this genus from 

 Sulcoretepora . H. canadensis is found in the Olentangy shale and the Silica 

 formation. 



Sulcoretepora ( Cystodictya of older publications) is like Hederella 

 but has a very different method of growth (fig. 166). There are not as many 

 branches as in Hederella but the branches are stouter. See figures 165 

 and 166. 



Fistulipora is leaf-like and forms crusts on other objects. It lacks the 

 the lace -like openings of the next two genera. Two species are recorded for 

 our Devonian. 



Fenestrellina ( Fenestella of older publications) has already been de- 

 scribed in the Silurian chapter (fig. 98). Several species are found in our 

 Devonian rocks. 



Semicoscinium has also been described in the Silurian chapter (fig. 97). 



Fig. 166 



