MOLLUSC A— GASTROPODA. 589 



8*. Whorls round, resting one against the other without impression ; last 



part often loose-coiled k. 



k. Small, umbilicus moderate XLIX. Straparollina. 



k. Turbinate to discoid, umbilicus large L. Slraparollus. 



k. Minute, umbilicus minute LXVII. Cyciora. 



k. Minute, turbinate or discoidal umbilicus moderate (fresh- water 



type) CCXIV. Planorbis. 



8*. Whorls rounded, not in contact with each other 1. 



1. Without notch or keel LI. Phanerotinus. 



1. Notch or keel faintly developed LIX. Eccyliomphalus. 



8*. Whorls round except for impressed zone at the point of contact, m. 



m. Spire sunken into a flat surface or below it 77. 



77. Whorls flattened dorso-ventrally, umbilical margin notched. 



CVI. Solarium. 



77. Whorls not flattened , somewhat angular ff. 



ff. Many whorled, smooth CCXIV. Planorbis. 



ff. Few-whorled with lamellose growth lines. 



CCXII1. Vorticifex. 



m. Spire not sunken 88. 



88. Spire low, umbilicus large gg. 



gg. Whorls rapidly enlarging, umbilicus open or covered 



by callus XCIII. Teinostomata . 



gg. Whorls numerous, slowly enlarging, umbilicus open 



only in internal mold LXVI. Pycnomphalus. 



88. Spire moderately high hh. 



hh. Whorls strongly embracing ; umbilicus large, often 



covered 5f. 



5f . Lip interrupted at the body-whorl ; umbilicus 



large and deep CCXVIII. Archceozonites. 



5f. Lip continuous, not interrupted at the body whorl. 



2". 



2 f/ . Umbilicus large and round a''. 



a /r . Whorls few, round, rapidly enlarging, 

 umbilicus often covered by callus. 



CXI II. Natica. 



a". Whorls less rapidly enlarging, with a 



depressed sutural band, and generally 



an angulation around the umbilicus. 



CXIV. Gyrodes. 



2 // . Umbilicus small, whorls scarcely impressed. 



b". 



b". Small, smooth CXVIII. Valvata. 



LXVII. Cyciora. 

 b // . Large, with strong growth lamellae. 



LXXI. Holopea. 

 hh. Whorls moderately embracing or barely in contact or 

 even free. Internal molds of many naticoid shells 

 which may be non-umbilicate when perfect or may 

 be strongly embracing, or may have spirals or even 

 ribs. 

 7. Shell without umbili cus 9*. 



