PLATE XXV. 



PAGE 



Fig. 20. Helicancylus .equicostatus. Top view of the spiral. 141 



20 a. Front view of the spiral. 

 20 b, c, d. Three views of the straight limb. 

 20 e. Side view of the largest limb. 

 20/. Cross section of aperture. 



20 g. Septum. 



Fig. 21. DiPTYcnocERAS l^vis. 144 



21 a. Cross section of the two smaller limbs, at the point of fracture of the 



specimen. 



21 b. Septum. 



