4 ZONITIDJE. 



The want of sharply defined characters makes the division of 

 the family into generic and subordinate groups very unsatisfac- 

 tory, and authorities differ widely as to the systematic position 

 of many of the species. As most of these are known to us by 

 the shell only, whilst some of the groups are differentiated en- 

 tirely upon anatomical grounds, it is difficult to arrive at satis- 

 factory conclusions regarding them. In Pfeiffer's " Nomenclator 

 Heliceorum," many species are undoubtedly erroneously grouped, 

 but it is the only attempt recently made to arrange all the spe- 

 cies, and I believe that the host interests of science will be con- 

 served by adopting Pfeiffer as the basis of my classification, 

 correcting such errors as have been indicated, or are apparent to 

 me, and adopting such new groups MS have been proposed by 

 more recent systematists, but usually without attempting their 

 enlargement by incorporating additional species with them. 

 When I shall depart from this rule it will be generally on account 

 of the geographical distribution of a newly proposed group indi- 

 cating pretty conclusively the common origin of its assigned 

 species, and those not heretofore referred to it, but partaking of 

 its features. 



The monographer of the /onitidai has ample material for 

 his work in Pfeiffer's several volumes, " Mouographia Heliceorum 

 Yiventinm " and his " Nomenclator Heliceorum," in the beauti- 

 fully illustrated monograph of Reeve, " Conchologia Iconica," 

 the Helicidse of Kiister's " Conchological Cabinet," Pfeiffer's 

 " Novitates Conchologicai," Rossmassler's " leonographie," and 

 numerous other works and papers. 



Synopsis of Genera. 

 Genus NANINA, Gray, 1834. 



Shell dextral or sinistral, heliciform, usually rather thin and 

 polished, the periphery rounded or angulated,columellar lip short, 

 reflected, often covering the umbilicus, outer lip simple, sharp. 



Animal capable of complete retraction within its shell, the 

 mantle furnished with an anterior lobe often bilobate, and a 

 collar which is sometimes simple, and sometimes provided with 

 one or two lobules reflected upon the shell ; these mantle-lobes 

 possess some power of lateral movement and of expansion and 

 retraction. Foot long and narrow, subtruncate posteriorly and 



