On Some Echinoids from the Paleo-Cretaceous of the Yuasa District in the Kii Peninsula and of the Yatsushiro District in Kyushu

Abstract

Although a fairly large amount of Echinoidea, of Mesozoic age, occurs in Japan, they have not yet been described in detail., For years, the authors have worked to make a more complete collection of specimens and to specifically identify them., As a result, seven species of the Lower Cretaceous are described here, and information concerning their horizons and localities is given., Conclusions are briefly summarized as follows: (1) Seven species of echinoids from the Arita formation in the Yuasa district and the Yatsushiro formation in the Kumamoto district, of which three are new, are described; and distinctions between them are made., They belong to either of the two genera, Washitasier and Enallaster., (2) On the basis of zones of Ammonites, the ages of the Arita and Yatsushiro formations were found to be of the Barremian and Albian, respectively., Therefore, it is evident that both genera are also found in the Barremian., (3) The genus Washitaster is known to occur elsewhere in the Aptian., (4) The characteristics of fascioles and peristomes and positions of apical system are regarded as essential for making distinctions between the two genera, while shape and arrangement of ambulacral pores are practical characteristics for specific identification.,