The present work is a taxonomic revision of the so-called pennatae trigoniids from Japan, with an attempt to explain the evolutionary parallelism between Heterotrigonia and Apiotrigonia. 16 species belonging to the pennatae trigoniids are known from various localities of the Upper Cretaceous in Japan. They are classified into two genera (Apiotrigonia and Heterotrigonia) and four subgenera (Apiotrigonia s. str., Heterotrigonia s. str., Microtrigonia and Nakanotrigonia nov.). I propose Apiotrigoniinae nov. as a new subfamily of the Trigoniidae on these genera and subgenera together with several other genera and subgenera outside Japan, such as Columbitrigonia, ?Quoiecchia, Dampietrigonia nov. and Turkestanella nov. Apiotrigoniinae nov. is mainly composed of the Heterotrigonia trunk and the Apiotrigonia trunk which were probably derived from a common ancestor in the Lower Cretaceous. The evolutionary tempo of the Heterotrigonia trunk is more rapid than that of the Apiotrigonia trunk. Microtrigonia is an off-shoot of Apiotrigonia, whereas Nakanotrigonia nov. is that of Heterotrigonia. The apparently directional changes of characters are recognized in both trunks in parallel with each other.
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