Annals of the South African Museum

angles anterior anteroventrally appearance beaks become broad coarse commissure comprises concave concentric conocardiiformis Krauss convex Cooper crenulated Cretaceous crowded curved Description designation Diagnosis differs Discussion dorsal elongate escutcheon face faunas figured fine finely flank costae follow Formation genus Goldfuss growth rugae herzogi Hoepen holotype holubi Kitchin included interspaces Iotrigonia irregular Kitchin Kobayashi lanceolate Lateral view left valve marginal carina material maturity meet Megatrigonia moderately Myophorella Nakano narrow Neocomian nepionic stages nodate nodes Note oblique obsolete Occurrence opisthogyrous original ornament persists Pisotrigonia Port Elizabeth Museum posterior posteriorly primitive Pringle produced prominent Pterotrigonia radial references region relatively respiratory margin restricted Reyes ribs rounded rows separates Sharpe shell shoulder similar Skwarko slightly smooth South African Museum species specimens Steinmanella straight strongly subconcentric subfamily Superfamily Tashiro transverse transverse costellae trigonally Trigonia Trigoniinae tubercles Type umbones Upper Valanginian valve ventral margin weakly