594 NORTH AMERICAN INDEX FOSSILS. 



uu. Coiled throughout CXXI. Turritella. 



uu. Last whorls uncoiled CXXII. Vermetus. 



2222. Spirals numerous; spire short, few-whorled vv. 



vv. With two columellar plications. 



CXCVII. Tornatellcea. 



vv. With one columellar plication CXCVIII. Actceon. 



17*. Vertical sculpture dominant or equal to spiral w. 



w. With simple vertical ribs 3333- 



3333. Form slender, turritelloid, protoconch erect, reversed. 



CII. Turbonilla. 

 3333. Form more tapering, whorls more rounding. 



LXXXI. Loxonema. 

 3333. Short and rather solid, sutures scarcely impressed. 



CXXVI. Hypsipleura. 



w. With sharp, regular varices instead of ribs CV. Scalaria. 



w. With both ribs and spirals 4444- 



4444. Later whorls mostly with shoulder angle bearing spinose 



nodes ww. 



ww. Spire high and slender CXXVII. Melania. 



CXXX. Goniobasis. 



ww. Spire short, shell thick-set CXXIX. Pyrgulifera. 



4444. All whorls round xx. 



xx. Columella with tooth CIII. Chrysallida. 



xx. Columella without tooth CXXX. Goniobasis. 



CXXVII. Melania. 



VI. Shell umbilicated, surface smooth, whorls flat or gently convex, suture not 



impressed, aperture oval, protoconch dextral CI. Niso. 



G. Shells pleurotomarioid and murchisonioid, varying in form from naticoid or trochi- 

 form to high-spired, and characterized by a marginal notch or slit, often 

 continued backward into a slit-band. 



VII. Shell turritelliform, with slender spire of numerous whorls 14. 



14. Lip with deep notch but no slit 18*. 



18*. Band generally formed but rarely very prominent x. 



x. Aperture slightly produced anteriorly, no umbilicus. 



XLVI. Hormotoma. 



x. Aperture round, shell umbilicated XLVII. Ccelidium. 



18*. Band strong, between two pronounced ridges y. 



y. Very slender, surfaces flat between carina, whorls compressed. 



XLVIII. Solenospira. 



18*. Band on shoulder formed by slight flattening and angulation of 



whorl XXX. Ormospira. 



14. Lip with slit Murchisonia. 



VII. Shell relatively low-spired, apical angle varying from moderately acute (rarely 



less than 45 °) to moderately obtuse (rarely more than 120 ) 15. 



15. Whorls angulated, shoulder flat or gently concave (rarely gently convex). 



19*. 

 19*. Whorls embracing to angulation, forming more or less trochiform 



spire z. 



z. Peripheral angulation drawn out into smooth or spinous flange. 



XXVIII. Euomphalopteris. 

 z. Peripheral angulation not drawn out 5555- 



