Annals of the South African MuseumAnnale van die Suid-Afrikaanse Museum . rginate below in most genera;posterior left tooth marginal, weak or obscure; anterior left tooth moderatelystrong; right valve with two subequal, more-or-less symmetrically divergentteeth not borne on hinge plate; anterior marginal tooth very obscure in somespecies; main teeth with strong transverse ridges except in a few primitive forms;anterior myophorous buttress generally well developed. Discussion At present this superfamily comprises the families Gruenewaldiidae , Trigoniidae (Pleurotrigoniinae and Trigonii
Annals of the South African MuseumAnnale van die Suid-Afrikaanse Museum . rginate below in most genera;posterior left tooth marginal, weak or obscure; anterior left tooth moderatelystrong; right valve with two subequal, more-or-less symmetrically divergentteeth not borne on hinge plate; anterior marginal tooth very obscure in somespecies; main teeth with strong transverse ridges except in a few primitive forms;anterior myophorous buttress generally well developed. Discussion At present this superfamily comprises the families Gruenewaldiidae , Trigoniidae (Pleurotrigoniinae and Trigoniinae), Neotrigoniidae ( herein ex subfamily Neotrigoniinae Kobayashi) (Nototrigoniinae andNeotrigoniinae) and Prosogyrotrigoniidae (Praegoniinae and Prosogyrotrigonii-nae) (Fig. 2). The most primitive trigoniaceans are assigned to the family Gruenewaldii-dae nov., in which the hinge is myophorian, with only partially striated teeth,and the areal ornament is predominantly transverse (Newell & Boyd 1975). At LOWER CRETACEOUS TRIGONIOIDA FROM THE ALGOA BASIN. Fig. 2. Hypothesized relationships within the superfamily Trigoniacea. Character states:1 = shell trigonal with prominent marginal carina and escutcheon, flank costae concentric,radial ornament to area subordinate to transverse ornament, hinge myophorian; 2 = hinge tri-gonian, area with radial ornament, at least in nepionic stages; 3 = shell ovate, marginal carinaobsolete, beaks prosogyrous; 4 = area with concentric ornament; 5 = antecarinal sulcus verybroad, shallow; 6 = area very broad, flanks wholly or partly with radial costae; 7 = marginalcarina and ornament to area restricted to nepionic stages, flank costae terminate at antero-lateral shoulder in prominent tubercles. present only Gruenewaldia and Lyriomyophoria are assigned here and both arevery small. The trigonian hinge (Newell & Boyd 1975) first appeared in the mid-Triassic,derived from the gruenewaldiid condition. Almost immediately there was afundamental
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Keywords: ., bookauthorsouthafr, bookcentury1800, bookdecade1890, bookyear1898
