MISSISSIPPIAN FOSSILS 



101 



Our Mississippian species of Chonetes are less than half an inch wide. 

 The spines of the cardinal margin are distinctive but not always preserved. 

 C. glenparkensis (fig. 252) is abundant in places in the Logan. 



Fig. 252 



Derby ia crassa ( Qrthothetes in older publications) has 

 one flat and one convex valve that bulges prominently at the 

 beak (fig. 252a). The surface of both valves is marked by 

 fine, sharp ridges radiating from 

 the beak. It is found in the 

 Maxville and ranges upward into 

 the Pennsylvanian. 



Schuchertella (fig. 253) and 

 Schellwienella both have a semicircular outline, prolonged into 

 wing-like expansions on the hinge line in some species. If both 



valves are preserved, they may be separated by the convexity of the valves, but unfortunately 

 only separate valves are usually found in our Mississippian. Schuchertella is represented 

 by one species in the Cuyahoga and two in the Logan; two species of Schellwienella occur in 

 the Logan. 



PELECYPODA. Many genera of pelecypoda are represented in our Mississippian rocks 

 but the majority of them are rare. Only the commoner genera are listed in the following key. 

 For more detailed information, see Hyde (1953). 



Key to the Commoner Mississippian Pelecypods of Ohio 



(see p. 4 for use of keys) 



Shell scallop-like, with 2 distinct "wings"; 



height and length approximately equal .... Aviculopecten 

 Shell without "wings" 2 



Height and length nearly equal 3 



Height distinctly less than length 4 



Beaks large Grammysia 



Beaks small Palaeoneilo 



Exterior of shell with concentric ridges 5 



Exterior of shell without concentric ridges 7 



Shell with a ridge or angulation from the beak to the margin .... Grammysia 

 Shell without such ridge cr angulation 6 



One end of shell pointed ., Palaeoneilo 



Ends of shell not pointed Allorisma 



One end of shell pointed Nuculana 



Ends of shell not pointed 8 



Shell with ridge or angulation from the beak to the margin 9 



Shell without such ridge or angulation Parallelodon 



Beaks wide and low Sanguinolites 



Beaks narrow and high Sphenotus 



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) 



