62 



OHIO FOSSILS 



Fig. 97 



In Fenestrellina (fig. 98) the branches 

 are angulated but not keeled, and the cross- 

 bars are thin and narrow. _F. elegans is 

 abundant in the Cedarville. 



BRACHIOPODA. In the Silurian rocks 

 of Ohio, brachiopods are almost as abundant 

 as in the Ordovician. One species, Pentamer- 



Fig. 98 



us laevis , is especially large, some specimens reaching a length of 5 inches. Some beds are 

 closely packed with fine specimens of Cryptothyrella cylindrica to the exclusion of almost 

 everything else. Still others have a variety of forms which seems almost endless. The follow- 

 ing" key will help identify the commoner genera. 



Key to the Commoner Silurian Brachiopods of Ohio 



(see p. 4 for use of keys) 



Shell smooth or with concentric ornamentation only 2 



Shell with radiating and concentric ornamentation 6 



Shell longer than wide 3 



Shell as wide as long or wider than long 5 



Internal mold with a pair of stout prongs on each side Trimerella 



Internal mold without prongs , 4 



Beaks pointed Whitfieldella 



Beaks fat and round Cryptothyrella 



Surface covered with short spines Nucleospira 



Surface smooth Meristina 



Concentric ornamentation stronger than radial ornamentation 7 



Concentric ornamentation weaker than radial 8 



Shell bent downward at margin Leptaena 



Shell not bent downward at margin Plectodonta 



Shell with less than 40 radiating ribs 9 



Shell with more than 40 radiating ribs 19 



Shell with sinus and fold 10 



Shell without sinus and fold 18 



Hinge line more than half the width of the shell 11 



Hinge line less than half the width of the shell 12 



Concentric ornamentation leaf -like and spiny Crispella 



Concentric ornamentation not leaf -like Platystrophia 



Radial ornamentation of only a few (1 to 3) large folds, not ribs 13 



Radial ornamentation of more than 3 distinct ribs 14 



Width and height almost equal Gypidula 



Width much less than height Pentamerus 



1. 



a) 





b) 



2. 



a) 





b) 



3. 



a) 





b) 



4. 



a) 





b) 



5. 



a) 





b) 



6. 



a) 





b) 



7. 



a) 





b) 



8. 



a) 





b) 



9. 



a) 





b) 



10 



a) 





b) 



11 



a) 





b) 



12 



a) 





b) 



13 



■ a) 





b) 



