ADEORBIIDiE. 13 



Subgenus Trachydomia, Meek and Wortheu. 1866. 



Whorls regularly ornamented with small tubercles. N. nodosa, 

 Meek and AVorthen. Carboniferous. Illinois. 



Included in Naticidse (vol. viii, 8), but is better j^laced here 



Family ADEORBIIDM 



Shell umbilicated, auriform, depressed, paucis2:)iral, with oblique, 

 entire aperture, simple columella, and rounded, sharp outer lip. 

 Oj^erculum corneous, paucispiral, with excentric nucleus. 



Animal differing from Trochidse by having no cirriform appen- 

 dages of the foot. Dentition unknown. 



In this group are provisionally included a few small shells, the 

 relationships of which remain somewhat obscure. 



Genus ADEORBIS, S. Wood. 1842. 



Shell depressed, flattened below, white, sub translucent, paucis- 

 piral, periphery angulated, widely umbilicated; aperture oblique, 

 angular behind, lip sharp, not continuous. 



Europe, Japan, Philippines, West Indies, etc. A. hubcarinatus, 

 Mont. 



Genus ARCHYT^A, Costa. 1869. 



Turbinated, but little elevated, thin, widely and deeply umbili- 

 cated, very finely decussated, appearing smooth, apertui-e rounded, 

 with sharp, simple lip. Operculum corneous, smooth and flattened 

 .exteriorly, the spire slightly pi'ominent in the centre of the inner 

 side. A. DELiCATUM, Phil. Norway. 



Traehysma, Jefireys, 1878, is a synonym. 



Subgenus Pseudorbis, Monts. 1884. 



Scarcely unibilicated, aperture circular, surface spirally costate, 

 not cancellated. A. granulum, Brugn. Mediterranean. 



