EXPLANATION OF PLATE XLI. 



Page. 



FIG. 1. Athyris viltata 90 



la. Dorsal view. 

 Ib. Ventral aspect. 



Devonian, Hamilton limestone. 



* 



FIG. 2. Retzia mormoni 95 



2a. Side view 



2b. Dorsal aspect. 



2c. Ventral view. 



Carboniferous, Upper Coal Measures. 



FIG. 3. Rhynchonella dentata 100 



Ventral aspect. (Mus. Mo. Geol. Snr.) 

 Silurian, Trenton limestone. 

 FIG. 4. Retzia sp.1 



Dorsal aspect. (Mus. Mo. Geol. Sur.) 

 Carboniferous, Lower Burlington limestone. 



FIG. 5. Nucleospira pisiformis ; 94 



Ventral aspect. (Mus. Mo. Geol. Sur.) 

 Silurian, Niagara'? limestone. 



FIG . 7. Rhynchonella uta 108 



Ventral aspect. 



Carboniferous, Upper Coal Measures. 

 FIG. 8. Rhynchonella sp 1 



8a. Dorsal aspect . (Davis collection ) 

 8b. Side view. (Davis collection.) 



Carboniferous, Burlington limestone. 



FIG. 9. Athyris hannibalensis 91 



Ventral aspect. (Mus. Mo. Geol. Sur.) 

 Carboniferous ? Louisiana (Kindeihook) limestone. 



FIG 10. Athyris incrassatus. 91 



Dorsal aspect. (Mus. Mo. Geol. Sur ) 

 Carboniferous, Burlington limestone. 

 FIG. 11. Rhynchonella sp ? 



Dorsal view. (Keyes collection ) 

 Carboniferous, Kindeihook shales. 



FIG. 12. Rhynchonella capax 99 



12a. Dorsal view. (Mus. Mo Geol. Sur ) 

 12b. Side view. (Mus. Mo. Geol Sur ) 

 Silurian, Hudson River shales. 



FIG. 13. Atrypa reticularis 97 



13a. Side view. 

 13b Dorsal aspect. 



Devonian, Hamilton limestone. 

 FIG. 14 . Terebratula sp . 1 



Dor sal view. (Rowley collection ) 

 Carboniferous, Burlington limestone. 



FIG. 15. Terebratuta rowleyi 105 



Dorsal aspect. (Rowley collection.) 

 Carboniferous, Lower Burlington limestone. 



