▁imm ers ed ▁in ▁the ▁first ▁of ▁the ▁succeed ing ▁turns , ▁above ▁which ▁only ▁the ▁t ilt ed ▁edge ▁of ▁the ▁last ▁vol ution ▁projects , ▁which ▁is ▁marked ▁by ▁five ▁sl ender ▁spir al ▁threads . ▁The ▁four ▁wh or ls ▁of ▁the ▁tele o con ch ▁are ▁am ply ▁rounded , ▁slightly ▁con str icted ▁at ▁the ▁s ut ures ▁and ▁app ress ed ▁at ▁the ▁summ its . ▁They ▁are ▁marked ▁by ▁six ▁spir al ▁c ords ▁between ▁the ▁s ut ures , ▁of ▁which ▁the ▁second ▁and ▁third ▁below ▁the ▁sum mit ▁are ▁very ▁narrow , ▁occup ying ▁together ▁about ▁as ▁much ▁space ▁as ▁one ▁of ▁the ▁other ▁c ords . ▁These ▁c ords ▁are ▁separated ▁by ▁gro ov es ▁which ▁almost ▁equal ▁them . ▁The ▁ax ial ▁sculpt ure ▁is ▁reduced ▁to ▁fee ble ▁indic ations ▁of ▁rib s ▁which ▁are ▁best ▁shown ▁near ▁the ▁sum mit ▁of ▁the ▁wh or ls , ▁where ▁they ▁render ▁the ▁spir al ▁ke els ▁fe eb ly ▁nod ul ous . ▁About ▁twenty - two ▁of ▁these ▁rib s ▁appear ▁upon ▁the ▁pen ult imate ▁wh or l . ▁The ▁peri ph ery ▁and ▁the ▁base ▁of ▁the ▁body ▁wh or l ▁is ▁well ▁rounded . ▁It ▁is ▁marked ▁by ▁seven ▁spir al ▁ke els , ▁which ▁grow ▁success ively ▁we aker ▁from ▁the ▁peri ph ery ▁to ▁the ▁um bil ical ▁area . ▁The ▁channels ▁separ ating ▁the ▁c ords ▁are ▁narrow , ▁well ▁inc ised , ▁crossed ▁by