194 HELICIiY.E. 



paradoxa, Pj'eiff. Thersites, Broil. 



serena, Beck. tropidophora, Adams and 



Reeve. 



Sub-gen. oxtchona, Morch. 



Shell imperforate, trochiform, the last whorl angulated or 

 carinated, base flattened ; aperture quadrangular ; peristome 

 simple, acute, the columellar margin straight, dilated, the outer 

 infiexed in the middle. 



bifasciata, Burrow. Steursiana, Shuttl. 



Cleryi, Petit. 



Genus acavus, Montfort. 



Shell imperforate, obliquely ovato-globose ; whorls ra- 

 pidly increasing, the last ventrorsal ; aperture protracted, 

 very oblique, oblong; columella horizontal, wide, adnate by 

 an excavated callus to the basal margin ; peristome thick, 

 widely reflexed, the margins united by a diffuse, shining 

 callus. 



Syn. Hemitrochus, Swainson. 



E.v. A. nemoralis, Linnceus, pi. 77, fig. G. Shell, A. 

 heemastoma, Linnaus, fig. 0, a. 



Acavus, as restricted, is from Nicobar and the Island of 

 Ceylon ; the species of Tachea are chiefly European ; the 

 only species of Phasis is from the Cape of Good Hope ; 

 and Geotrochus is from Amboina, New Guinea, and the 

 Philippines. 



