MANUAL OF THE MOLLUSCA. 



Io, Lea, 1831. 



Synonyms, Melafusus and Ceriphasia, Swainson; Pleurocera 

 and Strepoma, Eaf. ; Trypanostonia, Lea ; Telescopella, Gray. 



Type, I. fluvialis, Say (Fusus). 



Animal with the mantle margin plain ; eyes at the base of 

 the tentacles, which are short ; operculum subspiral. 



Shell fusiform, inflated, conical or oval ; aperture produced 

 into a more or less obvious canal in front. 



Distribution, 100 species. North America. 



Sub-genera, Lithasia, Haldeman, 1840. Synonyms, Angi- 

 trema, Haldeman ; Potodoma, Sw. ; Glotella, Gray. 



Columella callously thickened above and below; base of 

 aperture notched. Distribution, 31 species. North America. 



Strephobasis, Lea, 1861 (Megara sp., A. and H. Adams'). 

 Shell with a retorse canal at the base of the squarish aperture. 



Distribution, 8 species. North America. 



Gyrotoma, Shuttleworth, 1845. 



Synonyms, Goniobasis, Lea, 1862 ; Euryccelon, Lea. 



Shell solid, oval, oblong, or turreted ; many forms resemble 

 Taludomus; aperture subrhomboidal, subangular in front, 

 without a canal ; columella frequently callously thickened 

 above ; operculum subspiral, as in Melania. 



Distribution, 289 species. United States. 



Fossil, 8 species. Eocene. North America. 



Sub-genera, Schizostoma, Lea, 1842 (Schizochilus, Lea ; Mela- 

 toma carinifera, Anthony) ; aperture with a slit in the upper 

 part of the outer lip immediately under the suture. Distribu- 

 tion, 27 species. North America. 



Meseschiza, Lea, 1864. Slit in the middle of the outer lip. 

 M. Grosvenori. Indiana. 



Paxadllhea, Bourguignat, 1865. 



Dedicated to Dr. Paladilhe. 



Shell somewhat resembling that of Acme ; test thin, crystal- 

 line, extremely fragile; base of aperture produced in front; 

 peristome continuous, thin, truncated; outer lip with a slit 

 towards the suture. 



Distribution, 3 species. Fresh-water deposits. Herault. One 

 of the species is living in the neighbourhood of Montpellier. 

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