. ▁The ▁base ▁is ▁concentr ically , ▁rather ▁deeply ▁fur row ed , ▁the ▁ 6 ▁fur rows ▁nar ro wer ▁than ▁the ▁interven ing ▁rid ges . ▁In ▁the ▁um bil icus , ▁which ▁per for ates ▁almost ▁to ▁the ▁a pe x , ▁all ▁of ▁the ▁wh or ls ▁are ▁visible , ▁enc irc led ▁by ▁an ▁ac ute ▁car ina . ▁The ▁a pert ure ▁is ▁sub quad rate , ▁n acre ous , ▁smooth ▁within , ▁and ▁has ▁a ▁gro ove ▁indicating ▁the ▁place ▁of ▁the ▁external ▁ke el . ▁The ▁col um ella ▁is ▁S - sh aped , ▁and ▁ends ▁in ▁a ▁bl unt ▁to oth , ▁before ▁which ▁there ▁is ▁a ▁small ▁ac ute ▁dent icle . ▁A bove , ▁the ▁col um ell ar ▁plate ▁is ▁call ous , ▁and ▁covers ▁a ▁small ▁portion ▁of ▁the ▁um bil icus . ▁The ▁pretty ▁mark ings ▁of ▁the ▁shell ▁consist ▁of ▁ob lique , ▁regular ▁wide ▁black ▁stre aks , ▁separated ▁by ▁spaces ▁as ▁broad ▁as ▁themselves , ▁on ▁a ▁white ▁ground . ▁ ▁Distribution ▁This ▁species ▁occurs ▁in ▁the ▁Pacific ▁Ocean ▁between ▁E cuador ▁and ▁Northern ▁Peru . ▁ ▁References ▁ ▁External ▁links ▁ ▁To ▁US N M ▁In verte br ate ▁Zo ology ▁M oll us ca ▁Collection ▁ ▁To ▁World ▁Register ▁of ▁Marine ▁Species ▁▁▁ ▁mel ale uc os ▁Category : G ast rop ods ▁described ▁in ▁ 1 8 4 4 <0x0A> </s> ▁South ▁F ork ▁is ▁a ▁former ▁settlement ▁in ▁But te