Three new species of the echinoid genus Monostychia Laube, 1869 from Western Australia

Abstract

Three new species of the extinct echinoid genus Monostychia Laube, 1869 are described from Western Australia. All are from the middle Miocene Colville Sandstone of the Eucla Basin and have historically been referred to this genus without description. These new taxa differ from previously described Monostychia species in several morphological features, such as size and shape but also in the number of post-basicoronal interambulacral plates developed in the oral paired interambulacrum, a feature considered taxonomically important at both genus and species level for clypeasteroids. The number of ambulacral plates in the paired and unpaired oral regions is also considered a potentially diagnosti..