108 



being placed near the base : and the aperture is 

 more rounded at top. 



c. with the volutions elevated into a spiral cone. 

 Helix Terebra. Turt. Diet. p. 62. fig. 55. 

 In stagnant waters, and slow rivers. 



89. PLANORBIS complanatus. Shell glossy, transpa- 

 rent, striolate, concave above, with the outer volu- 

 tion very convex and abruptly larger, and a strong 

 prominent obtuse keel near the base, flat beneath. 



Planorbis Sheppardi. Leach, Mollusc, p. 149. 

 Helix complanata. Linn. Syst. 



Shell seldom above half the size of the last, and is 

 readily distinguished by the above characters. 



In slow rivers, in Suffolk and Devon. 



90. PLANORBIS rhombeus. Shell dark horn-colour, 

 flattish above, rather convex beneath, with four 

 volutions ; the outer one comparatively larger, 

 with a sharp keel near the base. 



Helix rhombea. Turt. Diet. p. 47. 



