GENUS XXII. BULLA. 105 



the aperture tlie whole lengtli of the shell ; the right lip 



acute; no umbilicus at the base (see Bulla Ampulla, f. 65). 

 AciiATiNA. Shell oval or oblong ; the aperture entire, longer 



than wide ; the pillar smooth, truncated at the base (see 



Bulla virginea, f. 66). 

 VoLVARiA. Shell convoluted and cylindrical, without any 



projecting spire ; the aperture narrow, the whole length 



of the shell, with one or more folds at the base of the 



pillar (see Bulla cylindrica, f. 67). 



