ZONITID.&. 5 



glandular, the pore slit-like, often surmounted by M horn-shaped 

 protuberance. 



Distribution. About six hundred species have been described, 

 many of which are simply varietal forms; they inhabit the 

 tropical regions of the old world, Africa, Asia and its islands, 

 Philippines, Polynesia, etc. 



The Naninas are closely related to the genus Zonites, which 

 is largely American and European in distribution, although a 

 few of its species occur in countries inhabited by the former. 

 They may be distinguished from Zonites by a generally larger, 

 less polished, thicker shell, and by the animal having cervical 

 mantle-lobes, and frequently polishing appendages, by their 

 genital orifice close to the tentacle, and by the marginal teeth of 

 the radula being bicuspid ate. 



Subgenus ARIOPHANTA, Desmoulins, 1833. 



Shell sinistral, umbilicated, often -angulatecl on the periphery. 



Animal. Mantle without polishing lobes ; mucus-pore large, 



without coniform protuberance. East Indies. 



Subgenus C(ELATURA, Pfeiffer, 1817. 



Shell dextral, often spirally sculptured, umbilical region 

 excavated, im perforate, columellar lip straight, oblique. 



Mucous pore without horn, mantle-lobes but slightly developed. 



Is. of Mauritius and Bourbon. 



Subgenus ROTULA, Albers, 1850. 



Shell dextral, subperforate ; spire depressed conical, last 

 whorl carinated at the periphery ; columella very short, vertical. 



Mucous pore with but a slight protuberance ; mantle without 

 polishing lobes, left cervical lobe usually bipartite. 



Mauritius, India, East Indies. 



Section PACIIYSTYLA, Morch, 1852 (restricted). 



Colume41a thickened and flattened. 



Section STYLODONTA, Jan, 1832. 



Imperforate, rather solid, periphery subangulated ; basal 

 margin of aperture somewhat thickened, columella short, 

 oblique, bearing a fold-like tooth. 



Erepta, Albers, 1850, is a synonym. 



