274 CYCLOTIN^E. 



tions, and among loose stones and leaves in chalky and 

 barren regions, while some take up their abode in the 

 immediate vicinity of the sea. The structure of the oper- 

 culum, which varies in different typical forms, presents 

 peculiarities which afford valuable aids in our endeavours 

 to group the species ; the shells are usually turbinate, and 

 are generally covered with an epidermis, which is often 

 mottled and variegated with a reddish brown colour. As 

 in the Helicidte, the spiral cone which forms the shell 

 assumes very varied proportions, being sometimes plan- 

 orbular and depressed, as in Cyclotus, pupiform and ele- 

 vated, as in Megalomastoma, or heliciform and moderate, 

 as in Cycloj)horus. 



Sub-fam. CYCLOTIN^E. 



Operculum thick, formed of two laminsB with a groove 

 on the edge between them ; the inner layer horny, the outer 

 calcareous ; orbicular, of many gradually- enlarging whorls, 

 usually with a raised border on their outer edge forming 

 a spiral ridge or fringe ; nucleus central. 



Genus CYCLOTUS, Guilding. 



Operculum orbicular, testaceous, arctispiral, rather con- 

 cave externally, the whorls with the margins thickened and 

 elevated, nucleus sub-central. 



Shell discoidal or turbinately depressed, widely umbili- 

 cated; aperture entire, circular; peristome simple or double, 

 straight, expanded or reflexed. 



Syn. Poteria, Gray. Myxostomella, Gray. 



Ex. C. semistriatus, Sower by, pi. 85, fig. 1. Oper 



