TRACnELIPODA. 103 



Planorbis carinatus. — The Keeled Planorbis. Plate 

 XIII. fig. 11. Depressed ; upper side concave, with a keel 

 round the middle of the last volution. Three-fourths of an 

 inch in diameter. Inhabits the ditches and lakes of Europe. 



Genus 70 FLA^ ARIA.— Brown. 



Generic Character. — Shell discoid, depressed on both 

 sides ; the volutions conspicuous on either side ; spire 

 slightly produced above, and concave beneath ; aperture 

 ovate ; edges of outer lip acute ; no operculum. 



Planaria alba The White Planaria. Plate XIII. 



fig. 17. White, slightly wrinkled transversely ; outer lip 

 with a narrow margin behind. One-fourth of an inch in 

 diameter. Inhabits the coast of Dunbar, Scotland. 



FAMILY X. COLLMACEA. 



Shell spiral, but without any exterior projections, except 

 the additions of growth ; outer lip frequently reflected ; 

 tentacula of the animal cylindrical ; no operculum. Ter- 

 restrial. 



Section I. — Animals with two tentacula. 

 Genus l\.—CYChO%TOUA.— Lamarck. 



Generic Character. — Shell variable in shape ; volutions 

 rounded ; aperture circular, entire, and reflected in the adult 

 state ; a horny operculum. 



Cyclostoma elegans — The Elegant Cyclostoma. Plate 

 XIII. fig. 12. Ovate, conical, umbilicated; with elegant 

 transverse striae; volutions five, very convex; ash-coloured, 

 with three bands of brown spots. Half an inch long. In- 

 habits Europe. 



Genus'±—A\]RlQ\]h A.— Lamarck. 



Generic Character. — Shell suboval, or ovato-oblong ; 

 aperture longitudinal ; entire at the base and contracted 



