echinoids of the genus tetragramma agassiz (phymosomatoida) from the aptian sediments of the basab region, northwest of kerman, iran

the echinoid fauna of basab area (aptian), northwest of kerman, is fairly rich and diverse, represented by pygaulidae, acropeltidae, emiratiidae, toxasteridae, holectypidae, stomechinidae and saleniidae. four regular echinoid species, among which three are new, assigned to genus tetragramma agassiz, are described and illustrated in the present paper. the new species are tetragramma basabensis, t. depressum and t. tetratuberculatus. the diagnostic features of the species are chiefly the number of interambulacral tubercles on ambital plates, the size of apical disc and peristome, and also horizontal and vertical outlines of the test. the tetragramma specimens occur in association with a rich orbitolinid fauna and macro-invertebrates consisting of bivalves, brachiopods, corals and gastropods. associated micro-macro fauna suggest an aptian age for the sediments.