GASTROPODA— EUOMPHALIDJE. 



655 



More rapidly enlarging ; volutions less rounded below ; striae 

 often fasciculate and irregular. 

 Hamilton of New York. 



163. S. cyclostomus Hall. (Fig. 898.) 



Devonic 



Fig. 898. Straparollus cyclostomus. (After Hall, Geol. Iowa, I., 2.) 



Low-spired, of five or six round, gradually increasing smooth 

 volutions with circular aperture. 

 Hamilton of Iowa. 



164. S. hecale Hall. Upper Devonic. 

 Similar to S. rudis, but with the whorls more gently enlarging. 

 Chemung of New York and Pennsylvania. 



165. S. ammon Wh. and Whitf. (Fig. 899.) 



Mississippic. 

 Small ; whorls round, rising but little above plane Fig. 899. 



Of VOlution. Straparollus 



... . . , ,. ,■■«.. • ammon. (Mitt 



Kinderhook and Burlington of Iowa and Missouri ; K / 

 also western New York. 



66. S. planispira Hall. (Fig. 900, a, b.) 



Mississippic. 



Fig. 900. a, b, Straparollus planispira ; c-e, S. spergenensis. (After Whitfield, Am. 



Mus. Nat. Hist. Bull.) 



Small, with flat or scarcely concave spire of 5 or 6 slender, very 

 gradually enlarging, rounded, smooth volutions. 



St. Louis beds of Indiana. 

 167. S. spergenensis Hall. (Fig. 900, c-e.) Mississippic. 



Early whorls flat, later slightly depressed, umbilicus deep. 



St. Louis of Indiana and Missouri. 



