EXPLANATION OF PLATE LI. 



FIG. 1. Bellerophon sp .1 Page 



Apertural aspect. (Hare collection.) 

 Carboniferous, Upper Coal Measures. 



FIG. 2. Bellerophon bilobatu* ? 147 



Dorsal aspect. (Rowley collection.) 

 Silurian, Trenton limestone . 



FIG. 8. Bellerophon marcouanus 148 



Dorsal aspect. (Hare collection ) 



Carboniferous, Upper Coal Measures. 

 Fig. 4. Porcellia nodosa , 154 



Side view . (Rowley collection . ) 



Carboniferous, Burlington limestone. 



Fig. 5. Straparollus obtusus 157 



View from above. (Keyes collection ) 

 Carboniferous, Kinderhook beds . 



FIG. 6. Straparollus ammon 158 



View from above. (Rowley collection . ) 

 Carboniferous, Burlington limestone. 



FIG. 7. Omphalotrochus springvallensis 162 



View of type . (U.S. Nat . Mns . ) 

 Carboniferous, Kinderhook limestone. 



FIG . 8. Straparollus valvatiformis '. 157 



View from below. (Mus. Mo. Geol. Sur.) 

 Cambrian. 



FIG. 9. Straparollus latui 158 



View from above . ( Keyes collection . ) 

 Carboniferous, Burlington limestone. 



