Taxonomy and biostratigraphy of large New Zealand Pliocene Pectinidae (Phialopecten and Mesopeplum)

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Abstract
Members of the lineage of Chlamys (Phialopecten) are the most useful index species for identifying ages of Pliocene limestone, and have the following time range: C. (P). tolagaensis Marwick, Kapitean (rare); C. (P.) tripboohi ongleyi (Marwick), Opoitian; C. (P.) triphooki marwicki Beu, Waipipian; C. (P.) triphooki tripbooki (Zittel), Mangapanian and early Nukumaruan. A further useful index of Waipipian age is Meseopeplum crawfordi (Hutton). Through Pliocene time members of the Chlamys (Phialopecten) lineage evolved progressively larger size, stronger sculpture, more nearly equal ears, and a more strongly convex left valve than those of their antecedents, in response to lying on the sea bed on the right valve and swimming frequently. In formal taxonomy, Pecten accrementa Hutton, 1873 and Phialopecten thomsoni Marwick, 1965 are synonymised with Chlamys (Phialopecten) triphooki triphooki (Zittel, 1864), a new subgenus Mesopeplum (Borehamia) is proposed for M. crawfordi (Hutton), and Phialopecten hilli (Hutton) is transferred to Mesopeplum (Borehamia).