Suture modification by pectinirhomb growth in Lepadocystis decorus, a new species of callocystitid glyptocystitid rhombiferan (Echinodermata) from Illinois

A new species of Late Ordovician callocystitid rhombiferan (Glyptocystitida e), Lepadocystis decorus, is described from the Brainard Shale of north-cen tral Illinois. This species is characterized by five pectinirhombs, open in fralateral and lateral plate circlets, and well-developed ridges on the the cal prates. Lepadocystis decorus well illustrates that open vs. closed plat e circlets in glyptocystitids can largely be a function of pectinirhomb len gth and is therefore in part an ontogenetically linked characteristic. Cons equently, great care must be taken to assure maturity when using this featu re in taxonomy.