Documentation of a study of the Cretaceous Echinoids Cretaceous Echinoids from Northeastern Brazil is Number 31 within the Fossils and Strata series of monographs and memoirs in palaeontology and biostratigraphy. The international Fossils and Strata series features systematic and regional monographs with taxonomic descriptions. The series is owned by and published on behalf of The Lethaia Foundation with collaboration among the Scandinavian countries.