no 



OHIO FOSSILS 



9. 



a) 





t>) 



10. 



a) 





b) 



11. 



a) 





b) 



12. 



a) 





b) 



13. 



a) 





b) 



14. 



a) 





b) 



15. 



a) 





b) 



16. 



a) 





b) 



17. 



a) 





b) 



Sinus and fold simple 10 



Sinus with a median ridge, fold with a median groove Mesolobus 



Fold and sinus without ridges Punctospirifer 



Fold and sinus with several ridges Neospirifer 



Radiating ridges strong, extending from beak to margin Hustedia 



Radiating ridges weak near the beak, strong near the margin . . . Wellerella 



Beaks large and coiled; one valve larger than the other 15 



Beaks small, not coiled; valves almost equal in size 13 



Hinge line as great as or greater than the width of the shell; 



with spines Chonetes 



Hinge line narrower than the width of the shell; without 



spines 14 



Beaks scarcely projecting over the hinge line Derbyia 



Beaks clearly projecting over the hinge line Rhipidomella 



Length greater than width; large Echinoconchus 



Length less than the width 16 



Concentric and radial ornamentation equally strong 17 



Radial ornamentation stronger than the concentric 



ornamentation Linoproductus 



Concentric and radial ornamentation forming Wart-like bumps . . . Juresania 

 Concentric and radial ornamentation forming a network of 



square pits Dictyoclostus 



Qrbiculoidea has already been described (see fig. 237). Its regular outline distinguishes 

 it from Petrocrania whose outline is irregular. Three species have been recorded. 



Petrocrania resembles Qrbiculoide a (see fig. 237) but has a characteristic irregular out- 

 line. P. modesta is common in some beds. 



Fig. 297 



Compos ita is a neat little shell without radiating ornamentation. Its 

 strong concentric striae and well-marked sinus and fold are distinctive. 

 C. subtilita (fig. 294) is common to abundant. 



Lingula is distinguished from other Pennsylvanian genera 

 by its small beaks, the lack of a sinus and fold, and the fine but 

 distinct concentric striae. L. carbonaria (fig. 295) is common. 



Crurithyris ( Ambocoeli a of older publications) can be 

 identified by its prominent beaks and very unequal valves. C. 

 planoconvexa (fig. 296) is common. 



Phricodithyris ( Squamularia in older publications) is 

 characterized by concentric rows of small spines on each 

 valve. The spines are seldom preserved and without them the Fig. 296 



genus might be confused with Crurithyris except that Phricodithyris has 

 almost equally convex valves whereas Crurithyris has one almost flat valve. 

 P. perplexa (fig. 297) is abundant in some beds. 



