▁the ▁form ▁of ▁plan isp ir als , ▁although ▁there ▁were ▁some ▁hel ically ▁sp ira led ▁and ▁n ons pi ra led ▁forms ▁( known ▁as ▁heter omorph s ). ▁ ▁The ▁name ▁" am mon ite ", ▁from ▁which ▁the ▁scientific ▁term ▁is ▁derived , ▁was ▁inspired ▁by ▁the ▁spir al ▁shape ▁of ▁their ▁foss il ized ▁shell s , ▁which ▁somewhat ▁res emble ▁tight ly ▁co iled ▁r ams ' ▁horn s . ▁Pl iny ▁the ▁E lder ▁( d . ▁ 7 9 ▁AD ▁near ▁Pom pe ii ) ▁called ▁foss ils ▁of ▁these ▁animals ▁am mon is ▁corn ua ▁(" horn s ▁of ▁Am mon ") ▁because ▁the ▁Egypt ian ▁god ▁Am mon ▁( Am un ) ▁was ▁typically ▁dep icted ▁we aring ▁ram ' s ▁horn s . ▁O ften ▁the ▁name ▁of ▁an ▁am mon ite ▁genus ▁ends ▁in ▁- cer as , ▁which ▁is ▁Greek ▁( κ έ ρ α ς ) ▁for ▁" horn ". ▁ ▁Di agnostic ▁characters ▁ ▁Am mon ites ▁( sub class ▁Am m ono idea ) ▁can ▁be ▁distinguished ▁by ▁their ▁sept a , ▁the ▁div iding ▁walls ▁that ▁separate ▁the ▁ch amb ers ▁in ▁the ▁ph rag mo con e , ▁by ▁the ▁nature ▁of ▁their ▁s ut ures ▁where ▁the ▁sept a ▁joint ▁the ▁outer ▁shell ▁wall , ▁and ▁in ▁general ▁by ▁their ▁si ph un cles . ▁ ▁Se pta ▁▁ ▁Am m ono id ▁sept a ▁character ist ically ▁have ▁bul ges ▁and ▁indent ations