102 TRACHELIPODA. 



with the spire produced; aperture entire, oblong; the outer 

 lip acute ; the lower part of the outer lip rising on the colu- 

 mella, and there forming an oblique plait, which enters into 

 the aperture ; destitute of an operculum. 



Lymncea stagnalis. — The Pond Ltmn^a. Plate XIII. 

 fig. 9. Ovato-acuminate, with the last turn ventricose, and 

 subangulate above ; the spire tapering to a point ; the aper- 

 ture large ; the outer lip spreading, thin, transparent, and 

 horn-coloured. Two inches long. Inhabits the ditches 

 and ponds of Europe. 



Genus 67- — PHYSA. — Drapernaud. 



Generic Character Shell generally sinistral, convolute, 



oval, or oblong ; spire prominent ; aperture longitudinal, 

 contracted above ; columella twisted ; outer lip very thin, 

 acute, partly obtruding above the plane of the opening ; 

 destitute of an operculum. 



Physa fontinaUs. — The Fountain Physa. Plate XIII. 

 fig. 6. Volutions reversed, oval, diaphanous, glossy, horn- 

 coloured ; spire very short and rather acute. Half an inch 

 long. Inhabits the ditches and streams of Europe. 



Genus 68.— LUTEA.— ^/-omjw. 



Generic Character. — Shell globular; spire short, sub- 

 acute ; aperture ovate ; outer lip not continuous, slightly 

 inflected at the top, and acute at the base ; a little reflected 

 on the base of the columella, and subumbilicated. 



Lutea lacuna. — The Lake Lute a. Plate XIII, fig. 10. 

 Very diaphanous, slightly wrinkled, and of a greenish horn- 

 colour. Half an inch long. Inhabits ditches in Britain. 



Genus 69 PLANORBIS.— Zay/iarc^. 



Generic Character. — Shell discoid ; spire depressed or 

 flat; the volutions apparent on both sides; aperture oblong, 

 semilunar, very distant from the axis of the shell; margin 

 not reflected ; no operculum. 



