STROBILUS

bi bo is it li lo oi or os si so ti to us ut

bio bis bit bos bot bro bur bus but its lib lis lit lob lot obi oil orb ors ort our out rib rob rot rub rut sib sir sis sit sob sol sos sot sou sri sub til tis tor tub tui urb uts

bios birl biro bits blot blur boil bolt bort boss bots bout brio bris brit bros brut burl burs buss bust buts libs list lits litu lobs loss lost loti lots lour lout lust obis obit oils orbs orts ours oust outs ribs riot robs roil roti rotl rots rout rubs rust ruts sibs silo silt sirs sits slit slob slot slub slur slut sobs soil soli sols sorb sori sort sots soul sour sous sris stir stob stub subs suit tils tirl tiro toil tolu tori tors toss tour trio tubs tuis urbs