278 TROCHID^. 



Family TROCHID^. 



Shell turreted or conoid ; aperture rounded or oblong, not spread- 

 ing ; lips disunited posteriorly. 



Oeiius ADEORBIS, Searles Wood. 1842. 



Shell dcpressly conical, orbicular, deeply umbilicatcd ; whorls 

 few, not nacreous, flattened, smooth or striated, the last more or 

 less angulated at the periphery ; aperture transversely oval, peris- 

 tome interrupted ; inner lip sinuatcd, outer lip arcuate, simple, 

 acute. 



Adeorbis costulata. 



Margarita costulata, Moller, Ind. Moll. Gr. 8. 



Adeorbis costulata, Stimpson, Proc. Bost. Soc. iv, 14 (1851) ; Shells of New England, 32; 

 Check Lists, 4. 



It is minute, about one tenth of an inch in diameter, white, some- 

 what thick and rugged near the apex, the sculpture ajjpearing to 

 advantage only on the thinner and more delicate outer 

 whorl, which is convex, rounded, and covered with 

 prominent, crowded ribs. On the side of the wliorl 

 many of these ribs divide into two, thus occupying the 

 A. costulata. increased space ; and beneath, the ribs flow into each 

 other and gradually disappear without interrupting the live distant, 

 elevated, spiral striae on the umbilical half of the base. The umbil- 

 icus is deep. The aperture is rounded, with the peristome contin- 

 uous. The operculum is multispiral, of about eight volutions, of 

 which the outermost are testaceous, presenting a frosted appear- 

 ance ; the central volutions, occu])ying about one fourth of the diam- 

 eter, are corneous. In deep water off Cape Ann, Grand Manan 

 (IT. SlimpsoTi). 



Ocniis MARGARITA, Leacii. 1819. 



Shell conical, moderately elevated ; whorls few, sub-inflated ; 

 aperture rounded, imperfect posteriorly ; lip sharp ; umbilicus deep ; 

 operculum multi-spiral ; the nucleus central. 



