732 NORTH AMERICAN INDEX FOSSILS. 



Fig 



Turritella mortoni, three varieties and internal mold, X 2 A » d 1S mutation 

 postmortoni, X 2 A' (Md. Survey.) 



angulated just below the suture, aperture obliquely elliptical, 

 effuse ; inner lip somewhat folded, slightly reflected at the base. 

 Claibornian of Alabama, abundant. 



428. T. humerosa Conrad. (Fig. 1065.) Eocenic. 

 Whorls nearly flat in the center, with strong primary and fainter 



secondary spirals ; an angulation near the base, visible only in the 

 body whorl, and a strong subsutural thickening carinated by two 

 spirals. Aperture subquadrate. 



In the Aquia formation less common than T. mortoni. Mid- 

 wayan, of Texas, Alabama, Arkansas. 



429. T. tampae Heilprin. (Fig. 1066.) Oligocenic. 

 Center of whorls slightly concave with a zone of two sunken 



spirals or three spiral grooves, basal angle pronounced and slightly 

 carinate. Sutures scarcely depressed except final gerontic stages. 

 Whole surface of shell covered with fine, sharp but almost micro- 

 scopic spirals. 



Orthaulax bed of Florida, etc. 



430. T. gatunensis Conrad. (Fig. 1067.) Oligocenic. 

 Whorls convex, but convexity marred by three strong spirals. 

 Vicksburgian, and Orthaulax beds of Florida. Isthmus of 



Darien, Panama, Costa Rica, etc. 



