7O TABULAR SCHEME. 



Slit at crown Fissurella, 326, 327. 



Slit on anterior margin Emarginula, 329-332. 



Slit between crown and margin Puncturella, 328. 



Crown near front margin 



Streaked with blue Helcion, 325. 



Not streaked with blue Tectura, 319-321. 



Crown almost central Patella, 324. 



Crown quite central 



Without shelf Lepeta, 322. 



With triangular shelf Propilidium, 323. 



With spiral diaphragm Calyptrcca. 383. 



Shell toothed 



Sinistral 



'Mouth with clausilium Clausilia, 304-309. 

 Mouth ovate Balea, 303. 



Cylindrical 



Mouth ovate or lunate Pupa, 288-291. 

 Mouth angular Vertigo, 292-302. 



Depressed Helix (obvoliita), 277. 



Oval- 

 Mouth pyriform Cochlicopa, 310, 311. 

 M outh obliquely oval, shell transparent Carychium, 201, 

 Mouth narrow, pillar with folds Melampus, 202, 203. 



Shell coiled flat- 

 Mouth circular 

 Without rib Valvata, 441, 442. 

 Clasping periphery Homalogyra, 385, 386. 

 Thickened with rib Planorbis, 216-218, 225, 226. 



Mouth oval and oblique, or 

 Oval and angulated, or 

 Semilunar with rib, or 

 Two-thirds of a circle with rib Planorbis, 215-226. 



Mouth four-fifths of a circle, without rib, or 

 Quadrangular, or 

 Horseshoe-shaped Helix, 263-287. 



Shell a raised spiral 



Pillar projecting beyond mouth 

 Outer lip digitate Aporrhais, 455, 456. 



Outer lip not digitate 



Basal groove curved Cerithium, 443-446. 

 Basal groove straight Cerithiopsis, 447-45 1- 



Pillar not projecting 

 Apex divided into two Stilifer, 467. 

 Apex broken off short Truncatella, 399. 

 Outer lip slit Scissurella, 334. 



