88 PK0VISI0NAL AID TO THE STUDY OF TASMANIA!* MOLLUSCA. 



Genus Bissoina. D'Orb. (264-274) 

 Shell turreted, whorls numerous, ribbed or cancellated ; aperture 

 semi-lunar ; lip slightly thickened within, somewhat 

 expanded, faintly channeled anteriorly; operculum 

 corneous, thick, semi-lunar, pauci-spiral with an 

 interior process. Dist.— World-wide (marine). 

 Sub-Family Bissoin^e. 

 Shell small, ovate or elongate ; operculum pauci-spiral, not 

 provided with an internal process (marine). 

 Genus Bissoa. Frem. (275-289.) 

 Shell minute, white or horny, conical, pointed, many whorled • 

 smooth, ribbed or cancellated; aperture rounded - 

 peristome entire or continuous; outer lip slightly 



expanded and thickened; operculum sub-spiral. Dist, 



Universal (marine). 



Sub-Genus Setia. H. and A.. Adams. 

 Shell thin, oval-oblong, or sub-conic ; whorls few, ventricose 

 spotted ; spire short ; apex obtuse ; aperture sub- 

 orbicular. 



Sub-Genus Ceeatia. H. and A. Adams. 

 Shell sub-cylindrical, spirally striated, white, thin, sub-pellucid- 

 whorls rounded; summit of spire obtuse ; aperture 

 sub-oval ; peristome continuous ; the outer lip thin and 

 sharp. 



Sub-Genus Cingitla. Fleming. 

 Shell thin, elongated, smooth or spirally striate, spotted or 

 banded; aperture pyriform or oval ; outer lip sharp, with 

 an external varix. 



Sub-Genus Alvania. Eisso. 

 Shell oval, turbiniform ; spire rounded, usually cancellated; 

 aperture sub-circular ; crenulated within ; outer lip with 

 a marginal exterior varix. 



Sub-Family Hydrobiimi. 

 Shell very small, or of moderate size, never exceeding two- 

 fifths of an inch in length, globose, ovate or elongated 

 generally umbilicated or rimate, and covered with 'a 

 t>eriostraca,for the most part of an olive colour- whorls 

 numerous (4-8) smooth or rarely ribbed or carinated - 

 never cancellated; aperture more or less ovate or 

 rounded, rarely sub-acute or effuse anteriorly - 

 pentreme continuous ; outer lip usually simple and acute '- 

 operculum pauci-spiral, corneous. Dist.-Lakes, rivers 

 and lagoons, sea-level to 4,000 altitude ; mostly inhabiting 

 fresh water but some entering brackish water* 

 herbivorous. ' 



