PLATE XV. 



PAGE 



Fig. 21. Ptychoceras ^uadratus. 74 



Natural size. 



Fisr. 25. Crioceras latus. 76 



| Natural size. 

 a. Section of volution. 



Fig. 30. Ancyloceras. Sp. indet. 78 



a. Septum. 



| Natural size. 



