Subgenera of the Upper Triassic bivalve <i>Monotis</i>

Abstract

Abstract A two‐fold division into the subgenera Monotis Bronn s.s. and Entomonotis Marwick was never fully accepted because it was too coarse and associated together in M. ( Entomonotis ) species varying greatly in size, inflation, and sculpture. The five species‐groups that were proposed by Westermann and new data from New Zealand Monotis laid the basis for the present proposal of five subgenera. Monotis s.s. resembles the salinaria group; M. ( Entomonotis ) (type species M. richmondiana Zittel) includes the ochotica, subcircularis , and zabaikalica groups; M. ( Eomonotis ) n. subgen. (type species M. typica (Kiparisova ) is equivalent to the typica group; M. ( Maorimonotis n. subgen, (type species M. routhieri Avias) covers the calvata group of Grant‐Mackie; and M. ( Inflatomonotis ) n. subgen, (type species M. hemispherica Trechmann) is erected for a form previously included in the ochotica group. Two species cannot be classified subgenerically. Lower Jurassic species from eastern U.S.S.R. and Italy are tentatively placed in Lupherella Imlay. The dubious Scythian M. boreas öberg is the only species of other than Norian age retained tentatively in Monotis .