ny der ▁is ▁located ▁on ▁Illinois ▁Route ▁ 1 , ▁ ▁south ▁of ▁Marshall . ▁ ▁References ▁ ▁Category : Un in cor por ated ▁communities ▁in ▁Clark ▁County , ▁Illinois ▁Category : Un in cor por ated ▁communities ▁in ▁Illinois <0x0A> </s> ▁The ▁G rac il oc er at idae ▁is ▁a ▁family ▁of ▁na util oid ▁ce phal op ods ▁from ▁the ▁Middle ▁and ▁Upper ▁Ord ov ician ▁belonging ▁to ▁the ▁On c oc er ida , ▁character ized ▁by ▁ex og astr ic ▁c yr to con es ▁that ▁expand ▁slightly ▁or ▁moder ately ▁and ▁have ▁thin ▁w alled , ▁orth o cho antic ▁ ▁marg inal ▁or ▁sub vent ral , ▁tub ular ▁si ph un cles ▁( S weet ▁ 1 9 6 4 ). ▁ <0x09> ▁The ▁G rac il oc er at idae ▁was ▁proposed ▁by ▁R ous seau ▁F lower ▁in ▁ 1 9 5 0 ▁and ▁at ▁that ▁time ▁placed ▁in ▁the ▁Bass ler oc er ida ▁which ▁has ▁since ▁been ▁abandoned . ▁It ▁is ▁now ▁assigned ▁to ▁the ▁On c oc er ida ▁( S weet ▁ 1 9 6 4 ). ▁ ▁Ph y log eny ▁The ▁G rac il oc er at idae ▁are ▁most ▁likely ▁derived ▁from ▁the ▁Bass ler oc er at idae ▁( F lower ▁ 1 9 5 0 ) ▁from ▁which ▁they ▁differ ▁primarily ▁in ▁having ▁thin ▁rather ▁than ▁thick ▁connecting ▁rings . ▁They ▁are ▁also ▁the ▁most ▁likely ▁source ▁for ▁the ▁On c oc er