us . ▁The ▁color ▁of ▁the ▁shell ▁is ▁white ▁with ▁a ▁gray , ▁ol iv ace ous ▁p cri ost rac um , ▁the ▁aspect ▁much ▁like ▁a ▁st um py ▁B ela ▁Le ach , ▁ 1 8 4 7 . ▁The ▁s uture ▁is ▁distinct , ▁not ▁opp ress ed . ▁The ▁wh or l ▁in ▁front ▁of ▁it ▁is ▁slightly ▁con str icted , ▁s lop ing ▁to ▁a ▁prominent ▁ke el ▁at ▁the ▁shoulder . ▁This ▁slope ▁is ▁apparently ▁coinc ident ▁with ▁the ▁anal ▁fas ci ole ▁and ▁is ▁sculpt ured ▁only ▁by ▁cur ved ▁lines ▁of ▁growth ▁and ▁faint ▁indic ations ▁of ▁ax ial ▁rib s , ▁which ▁become ▁more ▁prominent ▁in ▁front ▁of ▁the ▁shoulder . ▁They ▁become ▁stronger ▁on ▁the ▁earlier ▁wh or ls ▁and ▁number ▁about ▁fifteen ▁on ▁the ▁pen ult imate ▁wh or l . ▁These ▁rib s ▁are ▁fee ble , ▁with ▁wider ▁inter spaces , ▁rounded , ▁and ▁protect ive , ▁becoming ▁ob sole te ▁on ▁the ▁base ▁and ▁most ▁of ▁the ▁body ▁wh or l . ▁The ▁spir al ▁sculpt ure ▁is ▁strong est ▁in ▁the ▁shoulder ▁ke el , ▁which ▁is ▁a ▁little ▁nod ul ous ▁where ▁it ▁cross es ▁the ▁rib s . ▁In ▁front ▁of ▁it ▁are ▁three ▁to ▁five ▁spir al ▁threads ▁( on ▁the ▁sp ire ) ▁of ▁which ▁the ▁second ▁is ▁strong est ▁and ▁faint ly ▁nod ul ous , ▁the ▁others ▁fe eb ler , ▁more ▁adjacent ▁and ▁simple ▁These ▁become ▁more ▁numerous ▁by