Section CALDWELLIA, H. Adams, 1873. 



Shell small, subtrochiform, fragile, translucent, with angular 

 periphery and simple aperture. 



Subgenus RHYSOTA, Albers, 1850. 



Shell dextral, often large and rather thick for the genus, not 

 transparent, base excavated around the umbilicus. 



Mantle without shell lobes, left cervical lobe bipartite ; mucous 

 pore surmounted by a corniform protuberance. 



East Indies, Philippines, Polynesia. 



Section RHYSOTA (restricted). 



Upper and lower surface of the shell similarly sculptured, 

 rugose, finely vermiculate or granular; periphery more or less 

 angulated. 



Section HEMIPLECTA, Albers, 1850. 



Shell granular or striated above, smooth or polished below. 



Section EUPLECTA, Semper, 1870. 



Shell striated or ribbed above. Cervical lobes of the mantle 

 developed, the left one divided ; shell lojbes rudimentary ; mucous 

 pore with a short horn. Philippines. 



Inozonites, Pfeiffer, 1883, may be placed here. 



Section ROTULARIA, Morch, 1872. 



Shell resembling Rotula. Mucous pore with a horn-shaped 

 protuberance. Nicobar Islands. 



Section TROCHONANTNA, Mousson, 1809. 



Shell thin, striated above, smooth below, spire conical, periphery 

 angulated. Polynesia. 



Section MARTENSIA, Semper, 1870. 



Shell conical, keeled, perforate, sculptured above, smooth 

 below. Right shell lobe wanting, left cervical lobe bipartite ; 

 mucous pore with a horn. East Africa. 



I think it ver} r doubtful whether the several African groups 

 proposed by Semper, Martens, Pfeffer, etc., ought really to be 

 separated from Trochonanina. Ledoulxia, Bourg., 1885, might 

 as well be united with Martensia for the present ; it is founded 

 upon very unimportant characters of the shell alone, and takes 

 for its type the variety albopicta of N. Mozambicensis, the latter 

 the typo of Marlensia. 



