MANUAL OF THE MOLLUSCA. 
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Io, Lea, 1831. 
Synonyms, Melafusus and Ceriphasia, Swainson; Pleurocera 
and Strepoma, Raf.; Trypanostoma, 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 cailously thickened above and below; base of 
aperture notched. Distribution, 81 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. 
GyYROTOMA, Shuttleworth, 18435. 
Synonyms, Goniobasis, Lea, 1862; Euryccelon, Lea. 
Shell solid, oval, oblong, or turreted; many forms resemble 
Paludomus; aperture subrhomboidal, subangular in front, 
without a canal; columella frequently callously thickened 
above; operculum subspiral, as in Welania. 
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. Grosvenort. Indiana. 
PALADILHEA, 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 lp with a slit 
towards the suture. 
Distribution, 3 species. Fresh-water deposits. Herault, On. 
of the species is living in the neighbourhood of Montpellier. 
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