This short note is primarily intended to focus the collectors' attention on the occurrence of in situ peristomial and perisproctal plates in irregular echinoids from the Upper Cretaceous of southern Limburg (The Netherlands). Some recent finds are briefly discussed. Collectors are kindly asked to examine specimens in their collections carefully and thoroughly for these plates and to inform the author about new finds. A scientific paper on the occurrence of such plates in holasterid echinoids of the type Maastrichtian is now in preparation.