▁pet ro lic us ▁as ▁a ▁bas al ▁c arch arod ont osa ur id ▁in ▁a ▁tr ich ot omy ▁with ▁E oc arch aria ▁and ▁a ▁cla de ▁compr ising ▁more ▁derived ▁c arch arod ont osa ur ids . ▁ ▁References ▁ ▁External ▁links ▁ ▁Category : C arch arod ont osa ur ids ▁Category : E ar ly ▁C ret ace ous ▁din osa urs ▁of ▁Asia ▁Category : F oss ils ▁of ▁China ▁Category : F oss il ▁tax a ▁described ▁in ▁ 1 9 7 3 ▁Category : T ax a ▁named ▁by ▁D ong ▁Z him ing ▁Category : P ale ont ology ▁in ▁X in ji ang <0x0A> </s> ▁Ox yst ele ▁mer ula ▁is ▁a ▁species ▁of ▁sea ▁sn ail , ▁a ▁marine ▁g ast rop od ▁m oll usk ▁in ▁the ▁family ▁Tro ch idae , ▁the ▁top ▁sn ails . ▁ ▁Description ▁The ▁height ▁of ▁the ▁shell ▁var ies ▁between ▁ 2 7   mm ▁and ▁ 4 0   mm , ▁its ▁diameter ▁between ▁ 3 5   mm ▁and ▁ 4 1   mm . ▁The ▁rather ▁de pressed ▁con oid al ▁shell ▁is ▁imper for ate . ▁Its ▁color ▁is ▁l uster less ▁pur pl ish - black . ▁The ▁con ical ▁sp ire ▁has ▁an ▁er oded ▁yellow ish ▁a pe x . ▁The ▁following ▁wh or l ▁is ▁spir ally ▁stri ate . ▁The ▁last ▁two ▁wh or ls ▁are ▁smooth . ▁The ▁six ▁wh or ls