72 TABULAR SCHEME. 



Shell thin- 

 Outer lip thick Bithynia, 430, 431. 

 Outer lip thin Hydrobia, 426-429. 



Shell moderately thick- 

 Length over an inch Viviparus, 439, 440. 

 Length under half-an-inch Rissoa, 400-424. 

 Mouth nearly circular Cyclostoma, 397. 



Shell solid and smooth Barleeia, 425. 



Shell solid, heavy, and striated Littorina, 387-391 



Mouth grooved or with a canal 

 Shell transparent Achatina, 312. 



Shell not transparent 

 Shell convolute 

 Spire hidden 

 Outer lip plain 

 Outer lip ribbed Cypraa, 457. 



Spire not hidden Marginella, 529. 



Shell fusiform with long narrow mouth 



Mouth smooth, outer lip notched Pleurotoina, 536-549. 



Mouth grooved Mangilia, 530-535. 



Mouth ridged, outer lip curved Lachesis, 510. 



Shell with a curved canal 



Pillar with fold at base Columbella, 511, 512. 

 Pillar with tooth at base Nassa, 513-516. 

 Pillar smooth 



Coarsely ribbed Buccinum, 517, 518. 



Finely striated Buccinopsis, 519. 



Shell with straight canal 



Canal covered Murex, 506, 507. 



Canal open 

 Pillar smooth 



Canal long 



Shell measuring over an inch Fusus, 520-528. 



under an inchTrophon, 503-505, 

 Canal short Purpura, 508, 509. 



Pillar folded or tuberculated 



Shell with disconnected varices Triton, 459, 460. 



Mouth with merely an indistinct notch 



Shell without longitudinal ribs, cavity at base of 



pillar Trichotropis, 380. 



Shell without ribs, globose and finely striated 

 Torellia, 381. 



