PLATE XIII. 



Page. 

 Figs. 1-5. Pkonorites cvclouihis Phillips 43 



Ural Mountains. 

 Fig. 1. Side view. 



Fig. 2. "Crosa section of a volution, Tbergiceras stage." — Karpinsky. 

 Fig. 3. "Cross section of a volution, Faraprolecanites stage." — Karpinsky. 

 Fig. 4, a, b. Natural size. 



Fig. 5, a-f. Showing development of the sutures, from the Ibergiceru^ to the Proiiorites 

 stage. 



Figs. 6-15. GASTRnx-EU.\s listeki Martin 93 



Middle Coal Measures, Boles, Ark. 

 Fig. 6. Side view. 

 Fig. 7. Rear view. 



Fig. 8. Front view. Artificial east, magnified twice. 

 Fig. 9. Side view. 



Fig. 10. Side view, largest specimen. 

 Fig. 11. Cross section of whorl. 

 Fig. 12. Artificial cast. 

 Figs. 13-15. Development of the sutures. 

 Note. — Figs. 1-5 formed part of PI. XXIV, Proc. Am. Philos. Soc, Vol. XXX \', from 

 Ammoneen der Artinsk-Stufe, PI. I. 

 Figs. 6-15 formed PL XVI, Proc. Am. Philos. Soc, Vol. XXXV. 



174 



