MOLL USC A— GASTROPODA . 591 



8f. Inner lip thickened, shell thick. 



CXX. Campeloma. 

 8f. Inner lip not thickened, shell moderate. 



CXIX. Viviparous. 



333. Aperture elongate oo. 



00. Generally with distinct sutural shelf and smooth col- 

 umella CXV. Amauropsis. 



00. Without sutural shelf and with columellar fold. 



LXXXIX. Sphcerodoma. 



III. Surface with transverse striae or ribs ; or with spirals or with both 8. 



8. Shell umbilicated, umbilicus covered by callus of inner lip io*. 



IO*. Spirals or revolving plications most prominent, but not producing 



distinct shoulder angle p. 



p. Spirals or plications not uniformly distributed, shell partly non- 

 coiling LXXIV. Platyceras. 



p. Spirals more or less uniform, shell mostly or wholly coiled 



throughout 444. 



444. Whorls and aperture round, generally only touching 



without embracing pp. 



pp. Spirals much stronger than transverse sculpture. 



LXII. Poleumita. 



pp. Spiral sculpture not strong XCII. Margarita. 



444. Whorls more or less embracing, aperture round or irreg- 

 ular qq. 



qq. Strongly embracing 9f. 



9f . Whorls somewhat subangular, spirals smooth. 



XC. Gibbula. 

 9f. Whorls round, spirals regular, fine. 



CXI. Sigaretus. 



qq. Moderately embracing „ iof. 



lof. Spirals strongly nodose, spire elevated. 



LXIX. Trachydomia. 

 I of. Few spirals, not nodose, spire vertically com. 



pressed XCIV. Adeorbis. 



10*. Spirals faint or absent, transverse striae prominent q. 



q. Shell round -whorled, or more rarely angulated or even com- 

 pressed 555- 



555. Transverse striae straight and over entire shell. 



LXXIX. Callonema. 



555. Striae only on upper portion of shell LXXX. Isonema. 



8. Shell not umbilicated (rarely with faint umbilical indentation) II*. 



II*. Spirals pronounced, transverse sculpture weak or absent r. 



r. Lip discontinuous, whorls slightly impressed, spire acute to rect- 

 angular 666. 



666. Spirals numerous, nearly or quite impressed. 



LXIII. Cyclonema. 

 666. Spirals few, not of same size, one or more often beaded. 



XCI. Calliostoma. 



r. Lip continuous, outer lip sometimes reflected 777. 



777. Outer lip reflected and thickened. Columellar plications 

 present rr. 



