UMBONIINiE. 407 



Genus ADEOKBis, Searles Wood. 



Shell depressly conical, orbicular, deeply umbilicated; 

 whorls few, not nacreous, flattened, smooth or striated, 

 the last more or less angulated at the periphery ; aper- 

 ture transversely oval, peristome interrupted ; inner lip 

 sinuated; outer lip arcuate, simple, acute. 



Ex. A. subcarinata, Montagu^ pi. 45, fig. 7. 



The principal difference between this genus and Cyclo- 

 strema consists in the more or less trochiform appearance 

 of the shell, and in the peritreme not being circular and 

 continuous. A few species were described by one of the 

 authors under the generic name of Cyclostrema. 



Species of Adeorhis. 



elegans, A. Adams. porcata, Phil. 



plana, A. Adams. scabra, Phil. 



planorbula, A. Adams. subcarinata, Mont. 



Sub-fam. UMBONIIN^. 



Rostrum rudimentary ; frontal lobes greatly developed. 



Operculum horny, thin, of many gradually-enlarging 

 whorls finely ciliated on the outer edge. 



Shell orbicular, depressed, polished, porcellanous, the 

 umbilical region often covered with a callous deposit. 



Genus UMBONIUM, Link. 



Shell orbicular, depressed, porcellanous; whorls 

 smooth, polished, umbilical region covered with a large 



