PLATE XXI. 
Zone of Arietiies obtusus. 
Fig. 1. Arietites obtusus, Sowerhy 
All the specimens figured in this plate have a portion of the external lamina of the 
shell preserved, the surface is sculptured with longitudinal and transverse lines, which 
are finely punctated at their intersections. This kind of sculpture is rare, and found 
only, as far as I know, in Arietites obtusus, Sow,, Ar. stellaris, Sow., and Aegoceras 
PLANICOSTA, Sow. 
Side view, natural size. My collection. 
Front view, natural size. Do. do. 
Another larger specimen, natural size, 
collection. 
Side view, showing the extent of involution 
Lobe-lines, showing the lobes and saddles. 
