▁H ano i ▁National ▁University ▁of ▁Education , ▁Vietnam . ▁ ▁Distribution ▁ ▁Distribution ▁of ▁Per rott et ia ▁h ong th inha e ▁include ▁the ▁type ▁local ity ▁only . ▁It ▁is ▁in ▁Vietnam . ▁ ▁The ▁type ▁local ity ▁is ▁lim estone ▁for ests ▁in ▁Nam ▁Lo ong ▁Comm une , ▁La i ▁Ch â u ▁City , ▁La i ▁Ch â u ▁Province ▁in ▁Vietnam , ▁, ▁ 1 , 2 2 6 ▁m ▁a . s . l . ▁ ▁Description ▁The ▁shape ▁of ▁the ▁shell ▁is ▁ob lique - hel ic iform . ▁The ▁color ▁of ▁the ▁shell ▁is ▁white ▁and ▁transl uc ent . ▁The ▁shell ▁has ▁six ▁wh or ls . ▁The ▁sp ire ▁is ▁weak ly ▁convex . ▁Ap ical ▁angle ▁var ies ▁from ▁ 2 1 . 3 ▁to ▁ 2 4 . 8 . ▁S uture ▁is ▁distinct . ▁Sh ell ▁is ▁gl oss y ▁with ▁trans verse ▁rid ges ▁on ▁upper ▁surface . ▁Emb ry onic ▁shell ▁is ▁large , ▁with ▁about ▁ 2 ½ ▁wh or ls . ▁Sub sequ ent ▁wh or ls ▁are ▁regularly ▁co iled . ▁Body ▁wh or l ▁is ▁ax ial ly ▁def lect ed . ▁The ▁a pert ure ▁is ▁rect angular ▁with ▁rounded ▁angles . ▁Per ist ome ▁is ▁dis continu ous . ▁The ▁par iet al ▁call us ▁is ▁relatively ▁thick . ▁Lip ▁is ▁thick ened , ▁broad ly ▁expanded ▁and ▁reflected . ▁There ▁is ▁shall ow ▁sin ulus ▁present . ▁A pert